セミナー

The laser light shed on Darwin’s ‘Abominable mystery’

2024年10月10日(木) 16:00 - 17:00

加藤 千遥 (東京大学 大学院理学系研究科 生物科学専攻 博士課程)

Reproductive isolation is the inability of a species to breed with related species and thus is a key to evolution of new species in flowering plants. In interspecific crosses between closely related species, a stage of pollen tube reception by female tissues of the pistil act as a pivotal hybridization barrier. Within the genus Arabidopsis, pistils of Arabidopsis thaliana can be fertilized by pollen from its relative species, but about half of the ovules reject the release of sperm from heterospecific pollen tubes and these rejected pollen tubes continue growing inside the embryo sacs (referred to as pollen tube overgrowth). A loss-of function mutant line of ARTUMES gene, encoding a subunit of the oligosaccharyltransferase complex, pollinated with heterospecific pollen shows a higher overgrowth rate than the wild type, suggesting that ARTUMES is involved in interspecific pollen tube reception. However, its molecular mechanism is largely unknown. Here, we report that some knockout lines of receptor kinases show ARTUMES mutant-like impairment in interspecific pollen tube reception, indicating that these receptor kinases might be potentially the target proteins of ARTUMES. We anticipate these receptors recognize the ligands from conspecific (self) pollen and heterospecific pollen either in the presence of ARTUMES, thus they can lead successful interspecific fertilization. We also identified ARTUMES mutant shows abnormal calcium dynamics in their female tissue during pollen tube reception. In this talk, I would like to briefly mention about how mathematical modeling can be promoting to pursue the questions regarding calcium dynamics reflecting male-female communication during fertilization. We anticipate these mechanisms that enable interspecific fertilization contribute to rapid development and diversification of flowering plants in recent geological time.

会場: via Zoom

イベント公式言語: 英語

Joint Seminar on cosmology and related topics

2024年10月10日(木) 14:00 - 18:00

渡慶次 孝気 (東京大学 宇宙線研究所 (ICRR) 特別研究員)
辰馬 未沙子 (数理創造プログラム 研究員)
プトゥラク・ジャイアクソナ (数理創造プログラム 特別研究員)

Joint Seminar is a seminar series that is held regularly in Tokyo and its vicinity. The topics are on cosmology and related areas. The seminar venue alternates among the universities and research institutes in the Kanto area, and this time it is held at RIKEN. Among the 3 speakers in the event, Dr. Misako Tatsuuma and Dr. Puttarak Jai-akson from iTHEMS will give talks, together with an external speaker Dr. Koki Tokeshi (ICRR, U. Tokyo). The time table of the event is as follows: Date: October 10th (Thu), 14:30. (room will open at 14:00) Place: RIKEN iTHEMS Wako Campus, Okochi Hall Program: 14:00 Room open 14:30 Koki Tokeshi’s talk（ICRR, 45 min） 15:15 Break & free discussion（15 min） 15:30 Misako Tatsuuma’s talk（RIKEN iTHEMS, 45 min） 16:15 Break & free discussion（15 min） 16:30 Puttarak Jai-akson’s talk（RIKEN iTHEMS, 45 min） 17:15 Free Discussion（15 min） 17:30 Close (go to dinner) Titles and abstracts: 1st Speaker: Koki Tokeshi (ICRR) Title: Exact solutions in stochastic inflation Abstract: The stochastic formalism of inflation, or stochastic inflation for short, enables us to study the dynamics of large-scale primordial fluctuations in a non-perturbative way. I will present a class of all the possible exact expressions for statistical quantities such as distribution and correlation functions of a test field in the expanding universe, given that the significance of exact solutions in cosmology cannot be overemphasised. To this aim, a sequence of isospectral Hamiltonians and an underlying symmetry called shape invariance are exploited. 2nd Speaker: Misako Tatsuuma (RIKEN iTHEMS) Title: Numerical Simulations of the Strengths of Dust Aggregates in Planet Formation Abstract: Planet formation is the growth process from sub-micrometer-sized dust grains to planets larger than 10,000 km. This growth process can be broadly divided into two phases: the initial growth to kilometer-sized planetesimals, which involves the adhesion of dust grains through intermolecular forces such as van der Waals forces and hydrogen bonds, and the subsequent growth to planets, driven by gravitational forces. Currently, no unified planetesimal formation theory can fully explain both observations of protoplanetary disks, where planet formation takes place, and the exploration results of small bodies in the solar system, such as asteroids and comets, which are considered remnants of planetesimals. Constructing such a theory is the ultimate goal of planet formation studies. To investigate planetesimal formation based on the exploration results of small solar system bodies, we have used the discrete element method (DEM) to calculate the tensile and compressive strengths of dust aggregates, constructing their physically-based models that we have compared to the properties of small solar system bodies. This talk will focus on the methodologies used in these studies. 3rd Speaker: Puttarak Jai-akson (RIKEN iTHEMS) Title: Null Surfaces Through The Looking-Glass Abstract: Carrollian physics has recently become a prominent topic in theoretical physics, especially in gravitational studies and flat-space holography. Understanding Carrollian geometries and symmetries is essential to the modern interpretation of null surfaces, whether at finite distances or asymptotic infinities. In this talk, I will introduce Carrollian geometries as intrinsic to any generic null surface, and highlight the profound analogy between gravitational dynamics on null surfaces and Carrollian hydrodynamics. Additionally, I will discuss the phase space structure and symmetries associated with these geometries, shedding light on their implications for gravitational theories and potentially for holographic dualities.

会場: 大河内記念ホール

イベント公式言語: 英語

Understanding Diffusion Models by Feynman's Path Integral

2024年10月9日(水) 15:00 - 16:30

広野 雄士 (大阪大学 大学院理学研究科 物理学専攻 助教)

Diffusion models have emerged as powerful tools in generative modeling, especially in image generation tasks. In this talk, we introduce a novel perspective by formulating diffusion models using the path integral method introduced by Feynman for describing quantum mechanics. We find this formulation providing comprehensive descriptions of score-based diffusion generative models, such as the derivation of backward stochastic differential equations and loss functions for optimization. The formulation accommodates an interpolating parameter connecting stochastic and deterministic sampling schemes, and this parameter can be identified as a counterpart of Planck's constant in quantum physics. This analogy enables us to apply the Wentzel-Kramers-Brillouin (WKB) expansion, a well-established technique in quantum physics, for evaluating the negative log-likelihood to assess the performance disparity between stochastic and deterministic sampling schemes.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Dynamics of Phase Transitions: Between First and Second Order

2024年10月8日(火) 16:00 - 17:30

鈴木 史花 (CNLS Postdoctoral Research Associate, T4 / Center for Nonlinear Studies, Los Alamos National Laboratory, USA)

Phase transitions are typically classified as either first-order or second-order. The formation of topological defects in second-order phase transitions is well described by the Kibble-Zurek mechanism, while nucleation theory addresses first-order phase transitions. However, certain systems, such as superconductors and liquid crystals, can exhibit “weakly first-order” phase transitions that do not fit into these established frameworks. In this presentation, I introduce a new theoretical approach that combines the Kibble-Zurek mechanism with nucleation theory to explain topological defect formation in weakly first-order phase transitions. Additionally, I will discuss nonlinear quantum phase transitions that exhibit behaviors similar to weakly first-order transitions, which can be related to experiments with ultra-cold Rydberg atoms.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催 (メイン会場) / via Zoom

イベント公式言語: 英語

Application of Complex Scaling Method to Scattering Calculations of Atomic Systems

2024年10月8日(火) 13:30 - 15:00

佐野 大志 (早稲田大学 理工学研究科 物理学及応用物理学専攻 辻川研究室 修士課程)

Based on our paper [1], this presentation will show the application of complex scaling method(CSM) to scattering calculations of atomic systems. While CSM has been extensively used to study resonance states, the application of CSM to scattering calculations was proposed recently with applications in nuclear physics. In our study, we apply the CSM scattering calculation to atomic systems and propose an effective correction to avoid the problem of slow convergence to the number of complex eigen energies. Our results with the effective correction agree well with those reported in the literature for positron scattering with the targets Ne, Ar, Kr, Xe, H, He, He+, and Li2+. In this presentation, we introduce the framework of phase-shift calculation using the CSM together with the examples of the positron scattering, and advantages and features of this approach. [This seminar is co-hosted by Few-body Systems in Physics Laboratory, RIKEN Nishina Center.]

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Dense Matter Physics and Exotic States in Neutron Stars

2024年10月7日(月) 14:00 - 15:15

Vivek Thapa (Assistant Professor, Bhawanipur Anchalik College, India)

In the presentation, I will discuss the exploration of neutron star matter using phenomenological models, focusing on how exotic particles like antikaons, hyperons as well as Delta-resonances influence the neutron star equation of state (EoS). The discussion will cover how antikaon optical potentials and kaon condensation affect the stability and structure of neutron stars, as well as the potential for hadron-quark phase transitions leading to quark matter cores in massive stars. I will also highlight the study of non-radial oscillation modes which provide insights into the internal structure and composition of neutron stars. These oscillation modes are essential for understanding neutron star asteroseismology and interpreting gravitational wave signals from neutron star mergers. By comparing theoretical predictions with observational data, including mass, radius, cooling rates, and gravitational wave detections, the presentation aims to refine constraints on the EoS and enhance our understanding of dense matter in compact stars.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Clinical trials and standards of care: How doctors decide your medical treatment

2024年10月2日(水) 16:00 - 17:00

カトゥリン・ボシゥメン (数理創造プログラム 副プログラムディレクター)

Ever wondered what data is considered sufficient for approval of a new drug or vaccine? In this talk, I will talk about some of the errors and shortcomings with how clinical trials are run and regulated. I will also show how the data and analyses behind clinical trials can be very poorly done. I will show one example of very bad data and analysis, but I will also show an example of the valuable information that can come out of doing a good job in presenting, interpreting, and following the data. I will highlight how the over-reliance on summarizing measures like averages and the Gaussian assumption can lead to overlooking therapies that could otherwise have been extremely effective. This talk should be of critical importance to those working in the fields of health, medical and clinical research. But this talk is about data and its analysis, and as such is also very relevant to physicists and other scientists who generate, present or analyse data as part of their research.

会場: via Zoom / セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Organizational meeting 4

2024年9月26日(木) 16:00 - 17:00

This the semi-regular opportunity for iTHEMS Biology members to discuss their current research progress and/or difficulties and/or research questions. Anyone is welcome to join. It will be held in hybrid form.

会場: via Zoom / セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Renormalization Group Approach for Machine Learning Hamiltonian

2024年9月10日(火) 15:00 - 17:00

尾澤 岬 (CNRS Researcher, Laboratory for Interdisciplinary Physics (LIPhy), Université Grenoble Alpes, France)

We develop a multiscale approach to estimate high-dimensional probability distributions. Our approach applies to cases in which the energy function (or Hamiltonian) is not known from the start. Using data acquired from experiments or simulations we can estimate the underlying probability distribution and the associated energy function. Our method—the wavelet-conditional renormalization group (WCRG)—proceeds scale by scale, estimating models for the conditional probabilities of “fast degrees of freedom” conditioned by coarse-grained fields, which allows for fast sampling of many-body systems in various domains, from statistical physics to cosmology. Our method completely avoids the “critical slowing-down” of direct estimation and sampling algorithms. This is explained theoretically by combining results from RG and wavelet theories, and verified numerically for the Gaussian and φ4-field theories, as well as weak-gravitational-lensing fields in cosmology. Misaki Ozawa obtained his Ph.D. in 2015 from the University of Tsukuba. He did his first postdoc at the University of Montpellier in France. He then moved to Ecole Normale Supérieure (ENS) Paris as the second postdoc. Currently, he is a CNRS permanent researcher at Grenoble Alpes Univeristy in France. His background is in the physics of disordered systems such as glasses and spin glasses. He is also working on interdisciplinary studies between statistical physics and machine learning.

会場: セミナー室 (359号室) 3階 359号室 / via Zoom

イベント公式言語: 英語

A model to unify the theory of speciation

2024年9月5日(木) 16:00 - 17:00

ホセ サイード・グティエレス オルテガ (数理創造プログラム 基礎科学特別研究員)

Speciation, the process by which new species originate, occurs due to geographic (physical distance), ecological (different background environments), and historical (divergence time) factors that promote reproductive isolation among lineages. However, we don’t know how these factors interplay; therefore, our empirical and theoretical knowledge about speciation is limited, fragmented, and lacks unification. To fill this knowledge gap, I propose a model and an experiment that treats speciation as a continuum of the interplay between geographic and ecological factors. Empirical evidence has shown that the extremes of this continuum produce high evolutionary rate (faster speciation), while I expect that intermediate values in the interplay continuum would produce reduced evolutionary rates. I expect this seminar can open opportunities for collaboration.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Chromatophore patterns, packing, and scaling on a growing squid

2024年8月20日(火) 16:00 - 17:00

ロバート・ロス (沖縄科学技術大学院大学 (OIST) 生物複雑性ユニット / 計算行動神経科学ユニット 学際研究員)

Many biological patterns are formed during growth, and various modeling approaches have repeatedly shown that growth can substantially impact pattern formation. However, experimental testing of these ideas has been limited, largely due to the difficulty in precisely measuring organism growth while simultaneously tracking the dynamics of pattern formation. To address this, we turned to the skin of the oval squid. The oval squid grows rapidly, hatching with a length of approximately 16mm and reaching 90mm within 3 months. Throughout development, its skin is populated by pigment-filled cells called chromatophores. Following insertion into the skin, chromatophores do not move. This means that squid chromatophores, besides being the constitutive elements of a point pattern, can also function as reference points to precisely determine skin growth. For the more biologically-minded, I will explain how the chromatophore pattern emerges through the interplay of growth and decreasing chromatophore growth rates. For those who lean physics, I will talk about how due to the combination of volume exclusion and growth, chromatophores exhibit a scaling in which relative density fluctuations grow with spatial scale, akin to a critical system.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Social behavior and social engineering in bacteria

2024年8月1日(木) 16:00 - 17:00

Ashleigh Griffin (Professor, Department of Biology, University of Oxford, UK)

This year is the 60th anniversary of WD Hamilton’s seminal paper in which he outlined his theory of inclusive fitness and showed how it could be used to understand altruism in the social insects. In this talk, I will describe efforts made to use his theory to understand social behavior in bacteria. And I’ll go on to explore the potential of using these insights to tackle problems of antibiotic resistance in infections.

会場: セミナー室 (359号室) / via Zoom

イベント公式言語: 英語

Algebraic curves and parametric resurgence

2024年7月29日(月) 16:30 - 17:45

Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)

In this talk I will discuss recent work together with Ines Aniceto (Southampton) on algebraic examples of parametric resurgence. We discuss a simple example to elucidate the so-called higher order Stokes phenomena and discuss how a Borel inner-outer matching procedure allows us to view parametric resurgence as a series of non-parametric resurgence problems.

会場: 研究本館 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語