Search Event

Time-dependent bias emerges in population models with broad offspring number distributions

July 29 (Wed) 10:00 - 11:00, 2020

Takashi Okada (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

It has been increasingly recognized that natural populations exhibit broad offspring number distributions, either because offspring numbers are strongly variable (e.g. marine organisms) or because range expansion processes generate jackpot events. In this talk, I will review the basic concepts of theoretical population genetics and then discuss how broad offspring number distributions affect the evolutionary dynamics.

Venue: via Zoom

Event Official Language: English

Human Time vs. Mouse Time in Embryonic Development

July 17 (Fri) 16:00 - 17:00, 2020

Miki Ebisuya (Group Leader, European Molecular Biology Laboratory, Barcelona, Spain)

Different species have different tempos of development: larger animals tend to grow more slowly than smaller animals. My group has been trying to understand the molecular basis of this interspecies difference in developmental time, using the segmentation clock as a model system. The segmentation clock is the oscillatory gene expressions that regulate the timing of body segment formation during early embryogenesis. We have recently succeeded in recapitulating the segmentation clock from both human and mouse pluripotent stem cells, detecting oscillations and traveling waves in vitro. Interestingly, the oscillation period of human segmentation clock was 5-6 hours while that of mouse was 2-3 hours. Taking advantage of our in vitro system and simple mathematical models, we have been comparing the genome sequences and molecular processes of the segmentation clock between human and mouse to explain the interspecies difference in the oscillation period.

Venue: via Zoom

Event Official Language: English

Topological data analysis from a practical and mathematical perspective

July 15 (Wed) 16:00 - 18:10, 2020

Yuichi Ike (Researcher, Artificial Intelligence, FUJITSU LABORATORIES LTD.)

1. Topological data analysis and its applications In this talk, I will explain some methods in topological data analysis (TDA) and their applications. First I recall persistent homology, which is a central tool to analyze the "shape" of a point cloud set. Then I show several applications to material science and time-series analysis. I also talk about our collaborative research with Inria on noise-robust persistent homology and an automated vectorization method of persistence diagrams. 2. Persistence-like distance on sheaf category and displacement energy In this talk, I will talk about relation among sheaf theory, persistence modules, and symplectic geometry. We introduce a persistence-like distance on Tamarkin sheaf category and prove a stability result with respect to Hamiltonian deformation of sheaves. Based on this result, we propose a new sheaf-theoretic method to give a lower bound of the displacement energy of compact subsets of a cotangent bundle. This is a joint work with Tomohiro Asano.

Venue: via Zoom

Event Official Language: English

Complex Langevin study of an attractively interacting two-component Fermi gas in 1D with population imbalance

July 10 (Fri) 13:30 - 14:30, 2020

Shoichiro Tsutsui (Special Postdoctoral Researcher, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

We investigate an attractively interacting two-component Fermi gas in 1D described by the Gaudin-Yang model with population imbalance. While the Gaudin-Yang model is known as a solvable model based on the thermodynamic Bethe ansatz, the binding energy and mass of poralon at finite temperature and moderate impurity density are still unknown. Moreover, in such a system, quantum Monte Carlo simulation suffers from the sign problem because the population imbalance makes the fermion determinant non-positive definite. In this study, we apply complex Langevin method, a holomorphic extension of the stochastic quantization to overcome the sign problem. We first confirm our numerical results satisfy a criteria for correct convergence [1], and present how the polaron energy depends on temperature and density of impurity. We also compare our results with a recent study based on a diagrammatic approach [2].

Venue: via Zoom

Event Official Language: English

Constrained evolution of animal embryogenesis

July 8 (Wed) 10:00 - 11:00, 2020

Yui Uchida (Special Postdoctoral Researcher, Laboratory for Multiscale Biosystem Dynamics, RIKEN Center for Biosystems Dynamics Research (BDR))

Animals have developed a great variety of morphologies during the course of evolution. Despite this, phylogeny-specific features have sometimes been maintained for hundreds of millions of years, suggesting that there are constraints to morphological evolution. In my talk, I will introduce some of general motivations behind the EvoDevo study and talk particularly about the blank space in morphospaces (Each axis of a morphospace corresponds to a variable describing morphological features). It remains to be seen if these blank areas are caused by impossible developmental pathways. However, computer simulations of embryogenesis, which has been proposed in recent years, may provide a clue to a solution. Finally, I’m going to talk about my research plan based on this.

Venue: via Zoom

Event Official Language: English

iTHEMS Science Outreach Workshop 2020

July 3 (Fri) - 4 (Sat) 2020

RIKEN iTHEMS, an interdisciplinary Theoretical and Mathematical Sciences Program (RIKEN iTHEMS), was established in November 2016. RIKEN iTHEMS aims to use interdisciplinary methods with a focus on mathematics to elucidate the universe, matter and life, and to solve fundamental problems in society. Building on the achievements of the past exchanges through the Journalist in Residence Program, we will hold an outreach workshop to explore the relevance of the research of the RIKEN iTHEMS to society and to discuss how to build interactive relationships between journalists and researchers in the future. This year's workshop will be held by ZOOM as the seminar house is closed. Contact: Takashi Tsuboi (iTHEMS Deputy Director)

Venue: via Zoom

Event Official Language: Japanese

Waveform Analysis of Biological Rhythms

July 1 (Wed) 10:00 - 11:00, 2020

Shingo Gibo (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

Nonlinear oscillatory phenomena often emerge in various systems, for example circadian rhythms in biological systems and acoustic vibrations in engineering. Analysis and control of these oscillatory phenomena are one of the big problems in science and technology. My main research field is biological oscillations, especially circadian clocks. The circadian clocks are based on gene-activity rhythms with approximately 24-hour period, and its temporal waveforms are of various shapes. Recently, we theoretically showed that the period of circadian clocks is proportional to the waveform distortion from sinusoidal waves. Interestingly, we found the waveform is important for periods not only in biological oscillations but also in several other types of nonlinear oscillator models.

Venue: via Zoom

Event Official Language: English

iTHEMS Intensive Course [5] : "Adaptive strategies of organisms, their mathematical bases" - Evolution of cooperation

June 26 (Fri) 13:30 - 15:00, 2020

Yoh Iwasa (Senior Advisor, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Professor, Kwansei Gakuin University / Professor Emeritus, Kyushu University)

Living systems exhibit features distinct from nonliving physical systems: their structure and behaviors appear to be chosen adaptive. They are the outcomes of evolution. Mathematical formalisms developed in engineering and social sciences (e.g. control theory, game theory, evolutionary game theory) are sometimes very useful in biology.

Venue: via Zoom

Event Official Language: English

iTHEMS Intensive Course [4] : "Adaptive strategies of organisms, their mathematical bases" - Cancer as a mini-evolutionary process

June 25 (Thu) 15:00 - 16:30, 2020

Yoh Iwasa (Senior Advisor, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Professor, Kwansei Gakuin University / Professor Emeritus, Kyushu University)

Living systems exhibit features distinct from nonliving physical systems: their structure and behaviors appear to be chosen adaptive. They are the outcomes of evolution. Mathematical formalisms developed in engineering and social sciences (e.g. control theory, game theory, evolutionary game theory) are sometimes very useful in biology.

Venue: via Zoom

Event Official Language: English

iTHEMS Intensive Course [3] : "Adaptive strategies of organisms, their mathematical bases" - Masting, synchronized reproduction of trees: Coupled chaotic system

June 25 (Thu) 13:30 - 14:30, 2020

Yoh Iwasa (Senior Advisor, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Professor, Kwansei Gakuin University / Professor Emeritus, Kyushu University)

Living systems exhibit features distinct from nonliving physical systems: their structure and behaviors appear to be chosen adaptive. They are the outcomes of evolution. Mathematical formalisms developed in engineering and social sciences (e.g. control theory, game theory, evolutionary game theory) are sometimes very useful in biology.

Venue: via Zoom

Event Official Language: English

Universal Error Bound for Constrained Quantum Dynamics

June 24 (Wed) 16:00 - 18:10, 2020

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))

In quantum mechanics, the existence of large energy gaps allows us to trace out the degrees of freedom of irrelevant energy scale. Consequently, we can treat a system within a constrained subspace obtained by the projection of the total Hilbert space. While this statement has widely been used to approximate quantum dynamics in various contexts, a general and quantitative justification stays lacking. In this talk, we show a universal and rigorous error bound for such a constrained-dynamics approximation in generic gapped quantum systems [1,2]. This universal bound is a linear function of time that only involves the energy gap and coupling strength, provided that the latter is much smaller than the former. If time allows, I will briefly talk about generalizations of our result to e.g., quantum many-body systems and open quantum systems.

Venue: via Zoom

Event Official Language: English

iTHEMS Intensive Course [2] : "Adaptive strategies of organisms, their mathematical bases" - Dynamic optimization models for growth and reproduction

June 19 (Fri) 13:30 - 15:00, 2020

Yoh Iwasa (Senior Advisor, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Professor, Kwansei Gakuin University / Professor Emeritus, Kyushu University)

Living systems exhibit features distinct from nonliving physical systems: their structure and behaviors appear to be chosen adaptive. They are the outcomes of evolution. Mathematical formalisms developed in engineering and social sciences (e.g. control theory, game theory, evolutionary game theory) are sometimes very useful in biology.

Venue: via Zoom

Event Official Language: English

iTHEMS Intensive Course [1] : "Adaptive strategies of organisms, their mathematical bases" - Sex expression and sex allocation of marine organisms

June 18 (Thu) 13:30 - 15:00, 2020

Yoh Iwasa (Senior Advisor, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Professor, Kwansei Gakuin University / Professor Emeritus, Kyushu University)

Living systems exhibit features distinct from nonliving physical systems: their structure and behaviors appear to be chosen adaptive. They are the outcomes of evolution. Mathematical formalisms developed in engineering and social sciences (e.g. control theory, game theory, evolutionary game theory) are sometimes very useful in biology.

Venue: via Zoom

Event Official Language: English

Information geometry of operator scaling

June 17 (Wed) 16:00 - 18:10, 2020

Tasuku Soma (Research Associate, Graduate School of Information Science and Technology, The University of Tokyo)

Matrix scaling is a classical problem with a wide range of applications. It is known that the Sinkhorn algorithm for matrix scaling is interpreted as alternating e-projections from the viewpoint of classical information geometry. Recently, a generalization of matrix scaling to completely positive maps called operator scaling has been found to appear in various fields of mathematics and computer science, and the Sinkhorn algorithm has been extended to operator scaling. In this study, the operator Sinkhorn algorithm is studied from the viewpoint of quantum information geometry through the Choi representation of completely positive maps. The operator Sinkhorn algorithm is shown to coincide with alternating e-projections with respect to the symmetric logarithmic derivative metric, which is a Riemannian metric on the space of quantum states relevant to quantum estimation theory. This talk is based on joint work with Takeru Matsuda.

Venue: via Zoom

Event Official Language: English

Field theoretical approach to relativistic hydrodynamics

June 12 (Fri) 13:00 - 14:30, 2020

Masaru Hongo (Visiting Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Postdoctoral Research Associate, Physics Department, The University of Illinois at Chicago (UIC), USA)

Hydrodynamics is a low-energy effective theory of a conserved charge density, which describes a long-distance and long-time behavior of many-body systems. It is applicable not only to a non-relativistic weakly-interacting dilute gas but also a relativistic strongly-interacting dense liquid like a quark-gluon plasma. The main purpose of this seminar is to explain how we can derive the hydrodynamic equation from the underlying field-theoretical description of systems [1-3]. Our derivation is based on the recent development of non-equilibrium statistical mechanics, and we show that the procedure to derive hydrodynamic equations is similar to the so-called renormalized/optimized perturbation theory. Also, to describe transport phenomena in local thermal equilibrium, we give a path-integral formula for a thermodynamic functional, which results in the emergence of thermally induced curved spacetime [2]. These results enable us to derive hydrodynamic equation based on quantum field theories.

Event Official Language: English

Quantification model of energy of loop structure on biopolymer

June 3 (Wed) 10:00 - 10:45, 2020

Hiroshi Yokota (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

During cell division, the chromatin fiber condenses into a rod-like shape, which is the so-called chromosome. The chromosome is constructed by consecutive chromatin loop structures whose excluded volume interaction gives chromosome its stiffness. So far, the energy source for the loop growing has remained a controversial issue. In this seminar, we quantify the energy source by calculating the free energy difference before and after a model polymer chain creating a loop structure.

Venue: via Zoom

Event Official Language: English

How many electrons can atoms bind?

May 13 (Wed) 16:00 - 18:10, 2020

Yukimi Goto (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

In this talk, I will introduce the mathematical studies on the ionization problem. Some experimental & numerical evidences say that any doubly charged atomic ion X^{2-} is not stable. This 'fact' is called the ionization conjecture in mathematical physics literatures. My hope is to illustrates the interplay between mathematical and physical ideas. The talk is directed towards researchers on various aspects of quantum mechanics. In the first part, we will discuss the many-body aspects of quantum mechanics and introduce some basic notions. The second part will deal with the mathematical results in some approximation theories.

Venue: via Zoom

Event Official Language: English

Emergence of life in an inflationary universe

May 11 (Mon) 15:30 - 17:00, 2020

Tomonori Totani (Professor, Department of Astronomy, Graduate School of Science, The University of Tokyo)

The origin of life may be the greatest mystery in natural science. Especially, we know almost nothing about how the first biological molecule (possibly an RNA) appeared from abiotic chemical processes. A widespread notion is that the abiogenesis probability is extremely low when we consider only random chemical reactions to polymerize a large biological molecule. However, we do not know any more efficient polymerization process expected to work in a realistic prebiotic environment. Here, I consider this problem from a viewpoint of cosmology. Cosmologists agree that the universe created by an inflation should extend far beyond the observable universe (13.8 billion light year radius). Then the inflationary universe may be sufficiently large to produce many abiogenesis events, even if we consider only the basic random polymerization. I will give a quantitative answer to this question, and discuss various implications about the origin-of-life studies.

Venue: via Zoom

Event Official Language: English

Slip or (k)not: Geometry and mechanical performance of physical knots

May 7 (Thu) 17:00 - 17:45, 2020

Tomohiko Sano (PD, École polytechnique fédérale de Lausanne, Switzerland)

Knots can impart unique mechanical function to filamentary structures, with examples ranging across length scales, including DNA, polymer-chains, shoelaces, climbing ropes, tennis racket, and surgical sutures. Even though knot theory has a long history of studies in the realm of mathematics, mechanics-based studies of physical knots are much rarer. The fundamental challenge in the understanding of their mechanics under a wide range of loading conditions stems from the fact that their topology, geometry, elasticity, and friction are all tangled ingredients. In this talk, combining experiments, simulations and theory, we present the recent progress on the predictive framework for the knot performance.

Venue: via Zoom

Event Official Language: English

iTHEMS x academist Online open to the public "World of Mathematical Sciences"

April 18 (Sat) 10:00 - 17:00, 2020

Yuki Yokokura (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Ryosuke Iritani (Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Hirotaka Irie (Visiting Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Assistant Manager, DENSO Corporation)
Nagisa Hiroshima (Visiting Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Assistant Professor, Department of Physics, Faculty of Science, University of Toyama)
Hiroyasu Miyazaki (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Akinori Tanaka (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

Venue: via Zoom

Event Official Language: Japanese