Patterns of fern community assembly throughout the American continent: Do the mechanisms of species diversification also vary with latitude?

2023年11月7日(火) 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)

The global latitudinal gradient of biodiversity, a pattern suggesting that the low-latitude (tropical) areas have more species than the high-latitude (temperate) areas, represents the most conspicuous pattern of correlation between the environmental/geographic variation and biodiversity distribution. Yet, the relative roles of all ecological, geographic, and historical variables that can explain the gradient are unclear. Specifically, it is because we do not have a clear link between latitude and the underlying mechanisms that originate and extinct species throughout the gradient. In other words, we lack a connection between the “macroevolutionary patterns" and “microevolutionary processes”. I am researching the community assembly of ferns from the American continent, as it seems to be a group that can give some answers to what causes the latitudinal gradient of biodiversity and how the gradient is related to the processes of speciation and extinction. Regarding the community assembly, as expected, I found that the fern community clearly follows the latitudinal gradient: the number of species and localities colonized by ferns decrease with latitude. Also, this pattern is associated to a strong phylogenetic structure: the community at each latitudinal area is dependent of the previously colonizing genera (in other words, genera tend to diversify within specific latitudinal spans; most of them are restricted to the tropics). These results suggest that the fern community from the American continent follows the latitudinal gradient, and that it is a good representer of this pattern. Then, using linear regressions, I tested some classical hypotheses that have been proposed to explain the latitudinal gradient (e.g., that tropical environments, being more thermodynamically active, promote higher speciation rates). However, my results so far, suggest that none of the previously proposed hypotheses give a satisfactory explanation: there is no a single factor that can link the gradient with the processes of speciation or extinction. Rather, my data suggest that to promote speciation, the relative roles of environmental differentiation, geographic isolation, niche divergence, and time since divergence between sister species pairs vary with latitude. For example, to become new species, species near the equator did not need much geographic isolation or niche divergence from their sister counterparts (i.e., near the equator, species pairs tend to be more sympatric and present higher niche overlap). I hope my talk can stimulate some discussion about how to approach and treat the data that I have compiled, and that we can create opportunities for further collaboration.

会場: via Zoom

イベント公式言語: 英語

Compact Star Solutions Beyond General Relativity

2023年11月7日(火) 13:30 - 15:00

沼尻 光太 (名古屋大学 大学院理学研究科 博士課程)

The neutron star solutions have been gathering attention. Their high compactness enables us to observationally access the information about extreme regimes of hadron physics. On the other hand, their strong gravity features bring up another possibility, gravity beyond general relativity (GR). Although GR has been a great success until now, the present scenario for our universe still has several problems, such as dark sectors and the quantum description of gravity. To tackle these problems, the modified gravity theories have been discussed for decades. Their modifications are expected to become noticeable in strong gravity regimes like compact stars. In this talk, I will discuss the configuration of the compact star solution under the F(R) gravity, one of the most popular and simplest modifications of GR. The background hydrostatic solutions are calculated with some F(R) models, which show non-trivial influences from the additional scalar DOF in this theory. The tidal deformation phenomenon is also considered to focus on another observable, tidal deformability. I will comment on how to utilize obtained observables to determine the gravity theory and the unknown equation of state simultaneously.

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

Mathematical modelling of the host response to inhalational anthrax across different scales

2023年10月31日(火) 16:00 - 17:00

ビバリン・ウイリアムス (Postdoctoral Fellow, School of Mathematics, University of Leeds, UK)

Inhalational anthrax, caused by the bacterium Bacillus anthracis, is a disease with very high fatality rates. Due to the significant risk posed if the bacterium was to be intentionally used as a bioweapon, it is important to be able to defend against such an attack and to make optimal decisions about treatment strategies. Mechanistic mathematical models can help to quantify and improve understanding of the underlying mechanisms of the infection. In this talk, I will present a multi-scale mathematical model for the infection dynamics of inhalational anthrax. This approach involves constructing individual models for the intracellular, within-host, and population-level infection dynamics, to define key quantities characterising infection at each level, which can be used to link dynamics across scales. I will begin by introducing a model for the intracellular infection dynamics of B. anthracis, which describes the interaction between B. anthracis spores and host cells. The model can be used to predict the distribution of outcomes from this host-pathogen interaction. For example, it can be used to estimate the number of bacteria released upon rupture of an infected phagocyte, as well as the timing of phagocyte rupture and bacterial release. Next, I will show how these key outputs can be used to connect the intracellular model to a model of the infection at the within-host scale. The within-host model aims to provide an overall understanding of the early progression of the infection, and is parametrised with infection data from studies of rabbits and guinea pigs. Furthermore, this model allows the probability of infection and the time to infection to be calculated. Building a model that offers a realistic mechanistic description of these different animal responses to the inhalation of B. anthracis spores is an important step towards eventually extrapolating the model to describe the dynamics of human infection. This would enable predictions of how many individuals would become infected in different exposure scenarios and also on what timescale this would occur.

会場: via Zoom / 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

International Workshop on Blockchain Technology: Blockchain Kaigi 2023 (BCK23)

2023年10月28日(土) - 29日(日)

The International workshop Blockchain Kaigi (Kaigi: Meeting, Conference) aims to bring together researchers and practitioners from various communities of science and technology working on areas related to FinTech, crypto-asset, and blockchain. On February 17th – 18th of 2021 the international workshop “Blockchain in Kyoto 2021 (BCK21)” was held at Kyoto University, and the following year on August 4th – 5th the international workshop “BCK22: Blockchain Kaigi 2022” was held at Tohoku University, both gathered many participants from all over the world and ended successfully. As the third step, the international workshop “BCK23: Blockchain Kaigi 2023” will be held on October 28th -29th, 2023 at RIKEN’s Kobe Campus (Kobe City). Topics for this international conference include, but are not limited to the following. Crypto assets, cryptocurrencies Blockchain technology, cryptography/mathematics B2B and B2C solutions Anomaly detection, cyber security Digital Asset Market, Central Bank Digital Currency CBDC smart contract Application to energy and environmental problems Application to financial inclusion, remittance and digital identity Innovation policy Legal and regulatory issues Network Science, Graph Theory, Mathematics of Hypergraphs

会場: SUURI-COOL (Kobe)

イベント公式言語: 英語

Searching for dark neutrinos through exotic Higgs decays at the ILC

2023年10月24日(火) 16:30 - 17:30

Simon Thor (Ph.D. Student, KTH Royal Institute of Technology, Sweden)

In this study we investigate the feasibility of detecting heavy dark neutrinos ($N_d$) through exotic Higgs decays at the proposed International Linear Collider (ILC), specifically in the channel of $e^+ e^- \to qq~ H$ with $H\to \nu N_d \to \nu~lW \to \nu l~qq$. Analyses based on full detector simulations of the ILD are performed at the center-of-mass energy of 250 GeV for two different beam polarization schemes with a total integrated luminosity of 2 $\mathrm{ab}^{-1}$. A range of dark neutrino masses between the $Z$ boson and Higgs boson masses are studied. The $2\sigma$ significance reach for the joint branching ratio of $BR(H\to\nu N_d)\cdot BR(N_d\to lW)$ is about 0.1\%, nearly independent of the dark neutrino masses, while the $5\sigma$ discovery is possible at a branching ratio of $0.3\%$. Interpreting these results in terms of constraints on the mixing parameters $|\varepsilon_{id}|^2$ between SM neutrinos and the dark neutrino, it is expected to have a factor of 10 improvement from current constraints.

会場: via Zoom

イベント公式言語: 英語

Topological Aspect of Adsorption Site Selectivity on Metal Surfaces

2023年10月24日(火) 13:30 - 15:00

辻 雄太 (九州大学 総合理工学研究院 准教授)

In this talk, the presenter will discuss which adsorption structure is preferred in the adsorption of atoms and molecules on metal surfaces based on the topology of the adsorption structures. The method of moments is used to analyze the electronic density of states of the surface. The third-order moment, which characterizes the skewness of the distribution of the electronic density of states, is related to the topology of the triangles at the adsorption interface. By further relating this to the change in energy of the system with the change in electron occupancy of the states, it is shown that it is possible to discuss the relationship between the type of metal and the topological features of the energetically stable adsorption structure.

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

A cluster algebra structure in the quantum cohomology ring of a quiver variety

2023年10月24日(火) 10:00 - 11:30

Yingchun Zhang (Postdoctoral Researcher, Institute for Advanced Study in Mathematics, Zhejiang University, China)

The Gromov-Witten theory of a quiver variety is expected to be preserved by quiver mutation according to Seiberg duality, which has been proved to be true for A-type and star-shaped quivers. Cluster algebra can be constructed for a given quiver via quiver mutation. The two subjects Gromov-Witten and cluster algebra seem to differ a lot. Howerver, when we move to the quantum cohomology ring of a quiver variety, Benini-Park-Zhao’s work “indicates” that there should be a cluster algebra structure in the quantum cohomology ring of the quiver variety. In this talk, I will introduce our recent work about the construction of such a cluster algebra structure in the quantum cohomology of a quiver variety. In particular, we will give a proof of the construction for A-type cluster algebra in quantum cohomology of a flag variety. This is a joint work with Weiqiang He.

会場: セミナー室 (359号室)

イベント公式言語: 英語

Toward inferring the equation of state from gravitational-wave astronomy

2023年10月18日(水) 14:30 - 16:00

久德 浩太郎 (京都大学 大学院理学研究科 准教授)

The property of supranuclear-density matter is an important question to be answered in QCD. One promising avenue is to study neutron stars with astronomical observations. For this purpose, gravitational waves have become an important tool after GW170817 that delivered information about the matter at a few times the saturation density. If future detectors improve the sensitivity at high frequency, we may be able to investigate the phase structure at further higher density via observations of postmerger gravitational waves or the absence thereof. In this talk, I will review the current understanding of the neutron-star equation of state and then discuss possible future directions based on our binary merger simulation. This seminar is a part of UKAKUREN seminar and jointly held by GW-EOS WG in iTHEMS.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Introduction to F-Theory

2023年10月18日(水) - 20日(金)

溝口 俊弥 (高エネルギー加速器研究機構 (KEK) 准教授)

This is the fifth event hosted by the Quantum Gravity Gatherings (QGG) Study Group at RIKEN iTHEMS. For this event, we have invited Professor Shun'ya Mizoguchi from KEK, Tsukuba, to deliver pedagogical lectures on the F-theory and its relation to particle physics. We aim for this event to provide insights to researchers in related fields. Originally, heterotic string theory was a promising candidate for describing our world, as it naturally incorporated Grand Unified Theory (GUT) based on an exceptional gauge group. However, heterotic theory encounters challenges in moduli fixing. On the other hand, type II theory has an advantage in moduli fixing, but realizing GUT proves to be challenging. The F-theory describes the strongly coupled type IIB string theory, fully utilizing string dualities. This theory appears to realize both the moduli fixing and GUT. Consequently, F-theory plays a central role in string phenomenology. Shun'ya is a leading expert in these areas. We are fortunate to have the opportunity to learn numerous insights into string theory as well as particle physics. This intensive lecture series is designed to be an interactive event. To facilitate this, the number of participants will be limited to approximately 30. The intensive talk will be given in a face-to-face blackboard style (in English, no online streaming) to encourage informal and lively Q&A discussions. The program will also include short talk sessions, where participants can present a 5-minute talk on a topic of their choice, including their research, reviews of specific works, or future study interests.

会場: 研究本館 4階 435-437号室

イベント公式言語: 英語

Population genetics in microchannels

2023年10月17日(火) 16:00 - 17:00

Anzhelika Koldaeva (沖縄科学技術大学院大学 (OIST) 生物複雑性ユニット 研究員)

Spatial constraints, such as rigid barriers, affect the dynamics of cell populations, potentially altering the course of natural evolution. In this paper, we investigate the population genetics of Escherichia coli proliferating in microchannels with open ends. Our analysis is based on a population model, in which reproducing cells shift entire lanes of cells toward the open ends of the channel. The model predicts that diversity is lost very rapidly within lanes but at a much slower pace among lanes. As a consequence, two mixed, neutral E. coli strains competing in a microchannel must organize into an ordered regular stripe pattern in the course of a few generations. These predictions are in quantitative agreement with our experiments. We also demonstrate that random mutations appearing in the middle of the channel are much more likely to reach fixation than those occurring elsewhere. Our results illustrate fundamental mechanisms of microbial evolution in spatially confined space.

会場: via Zoom

イベント公式言語: 英語

Do higher-order interactions promote coexistence in diverse ecological communities?

2023年10月10日(火) 10:00 - 11:00

Theo Gibbs (Ph.D. Student, Lewis-Sigler Institute for Integrative Genomics, Princeton University, USA)

A central assumption in most ecological models is that the interactions in a community operate only between pairs of species. However, two species may interactively affect the growth of a focal species. Although interactions among three or more species, called higher-order interactions, have the potential to modify our theoretical understanding of coexistence, ecologists lack clear expectations for how these interactions shape community structure. In this talk, I will analyze two different sets of assumptions for how higher-order interactions impact the dynamics of competing species and show that they lead to differing outcomes. When higher-order interactions are sampled from unconstrained probability distributions, they are unlikely to generate widespread coexistence. In fact, using an analytical technique from statistical physics, I will show many — though not all — of the qualitative rules derived for pairwise interactions still apply to the higher-order case. Higher-order interactions that have specific relationships with the underlying pairwise interactions, however, can stabilize coexistence in diverse communities. I will conclude by briefly discussing ongoing experimental work that seeks to determine whether or not the dynamics of annual plant communities are structured by higher-order interactions.

会場: via Zoom

イベント公式言語: 英語

Neutrino production in AGN cores: Constraints from Kinetic Plasma Simulations

2023年10月6日(金) 14:00 - 15:15

Amir Levinson (Professor, Tel Aviv University, Israel)

Accreting black holes power a variety of high-energy astrophysical systems. The activation and mode of operation of these engines has been subject of intensive research. In recent years the structure of the multi-flow emanating from the putative, giant black hole in the M87 galaxy was probed down to near horizon scales in unprecedented detail, shedding new light on the physics of accretion and the processes responsible for the formation and dissipation of relativistic jets by the black hole. I shall review recent progress in observational and theoretical studies of accreting black hole engines.

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

Progenitors and Explosion Properties of Supernova Remnants Hosting Central Compact Objects

2023年10月6日(金) 10:00 - 11:30

チェルシー・ブラウン (Ph.D. Student, Department of Physics and Astronomy, University of Manitoba, Canada)

Presented is a systematic, global study of Galactic supernova remnants (SNRs) hosting Central Compact Objects (CCOs) aimed at addressing their explosion properties and supernova progenitors. With the Chandra and XMM-Newton telescopes, a spatially resolved X-ray spectroscopy study is performed on seven SNRs that show evidence of shock-heated ejecta. Using an algorithm, we segmented each SNR in the sample into regions of similar surface brightness. These regions were fit with one- or two-component plasma shock model(s) in order to separate the forward-shocked interstellar medium from the reverse shock-heated ejecta which peak in the X-ray bands for elements including O, Ne, Mg, Si, S, Ar, Ca, and Fe. We subsequently derived the explosion properties for each SNR in the sample and found overall low explosion energies (<10^51 erg). To address their progenitor mass, we compare the measured abundances from our spectroscopic modelling to five of the most widely used explosion models and a relatively new electron-capture supernova model. Additionally, we explore degeneracy in the explosion energy and its effects on the progenitor mass estimates. However, no explosion models match all of the measured ejecta abundances for any of the SNRs in our sample. Therefore, we present our best progenitor mass estimates and find overall low progenitor masses (<=25 solar masses) and we highlight the discrepancies between the observed data and the theoretical explosion models.

会場: via Zoom

イベント公式言語: 英語

How is host-symbiont specificity determined? ---Host’s partner-choice mechanisms and symbiont’s motility

2023年10月3日(火) 16:00 - 17:00

菊池 義智 (国立研究開発法人産業技術総合研究所 (AIST) 生物プロセス研究部門北海道センター 研究グループ長)

Microbial symbiosis is omnipresent in animals and plants, playing a crucial role in the evolution of these organisms. While some organisms have developed mechanisms for vertical symbiont transmission, in most cases, these microbial partners are acquired from the surrounding environment, where the enormously diverse microorganisms inhabit. How, then, do these hosts ensure specificity with their symbiotic partners among such diverse environmental microorganisms? And how has this host-symbiont specificity evolved? We are addressing these questions using the bean bug Riptortus pedestris as our model. The insect acquires Caballeronia insecticola from the soil and symbioses with it in the gut crypts. Recently, we revealed that the entrance to the gut symbiotic organ is a narrow tube, just a few micrometers in diameter, filled with a mucus-like matrix. This constricted region helps the host insect select the symbiotic bacterium from the many other soil microbes. Notably, to pass through the constricted region, Caballeronia shows a unique motility called “drill motility”, where the bacterium wraps its flagella around its body. In this presentation, I will introduce the evolutionary process of both host insects and symbiotic bacteria and will discuss the pivotal role played by bacterial motility in the context of host-symbiont specificity.

会場: via Zoom

イベント公式言語: 英語

Interactions between Algebraic Topology and Representation Theory by Toric Code

2023年10月2日(月) - 4日(水)

ミンキュ・キム (Research Fellow, School of Mathematics, Korea Institute for Advanced Study (KIAS), Republic of Korea)

Toric code is an error correction code designed by Kitaev in late 1990’s, which contributes to the birth of topological quantum computation. The goal of these lectures is to introduce toric code and related mathematics. We will explain an interaction between low-dimensional topology and representation of Drinfeld double. Especially, we will encode several operations (e.g. braidings) on representations into topology and geometry on surfaces. If time allows, we will give an overview of how toric code arises from chain complexes, which will be the prequel of our talk at Tokyo-Seoul Conference on Oct 6. These lectures will be fundamental and concrete. We hope that the audience are familiar with basic concepts of finite groups and Hopf algebras. These lectures will be held from Oct 2 to Oct 4, each from 13:30 to 15:00, for a total of 3 lectures. Oct 2 (mon) Introduction to toric code. Oct 3 (tue) Introduction to non-abelian toric code. Oct 4 (wed) Further studies on toric code.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

第4回「医学と数理」研究会

2023年9月29日(金) - 30日(土)

近代から今日へと続く医学の進歩は、数学や物理といった基礎科学の発展と切り離すことができません。これまでiTHEMSでは、2019年に第一回目の「京大−ハイデルベルク大－理研ワークショップ『医学と数理』」をスタートさせ、2020年にはコロナ禍のため第二回目の研究会をオンライン開催しました。2022年には第三回『医学と数理』研究会をハイブリッド形式で開催しました。第四回目の『医学と数理』研究会は、ハイブリッド形式で9月29日・30日に東北大学・知の館で開催します。29日午後には医学と数理をつなぐ融合教育を国際的に推進している研究者を交えたセッションを企画しています。 詳細および参加登録は、関連リンクをご覧ください。 共催： 京都大学高等研究院(KUIAS) 医学物理・医工計測グローバル拠点 京都大学大学院理学研究科 附属サイエンス連携探索センター(SACRA) 理化学研究所 数理創造プログラム(iTHEMS) 東北大学知の創出センター

会場: 東北大学片平キャンパス 知の館 / via Zoom

Response to sounds in the cochlea of the inner ear

2023年9月26日(火) 16:00 - 17:00

太田 岳 (大阪大学 大学院医学系研究科薬理学講座統合薬理学 助教)

We hear sounds. The acoustic wave passes through the ear canal and oscillates the ear drum. The middle ear bones conduct the mechanical input into the cochlea, the primary sensory organ of hearing. A sensory epithelium, a sheet-like tissue inside the snail-like structure, decomposes the sound frequencies into each component along the coil. The sound stimulation evokes nanometer-scale motions in the epithelium which contains hair cells. The cells expose their hair bundles to endolymph, the extracellular solution characterized by high [K+]. The epithelium vibration changes the open probability of mechanosensitive channels on the bundles and modulates the ion entering from the fluid. Inner hair cells release neurotransmitters to the auditory nerves and outer hair cells shrink and elongate their soma depending on the receptor potentials. The electromotive response amplifies the vibration of the sensory epithelium and contributes to the faint sound sensitivity and sharp frequency selectivity. With developed technique, we observed the sound-evoked vibrations in the sensory epithelium. In this seminar, I will introduce the physiological background of the cochlear physics and the recent results.

会場: via Zoom

イベント公式言語: 英語

Thermal production eV dark matter with bose-enhancement

2023年9月25日(月) 15:00 - 16:30

殷 文 (東北大学 大学院理学研究科 物理学専攻 助教)

A very simple production mechanism of feebly interacting dark matter (DM) that rarely annihilates is thermal production, which predicts the DM mass around eV. This has been widely known as the hot DM scenario. Despite there are several observational hints from background lights suggesting a DM in this mass range, the hot DM scenario has been considered strongly in tension with the structure formation of our Universe. In this talk, I show that the previous conclusions are not always true depending on the reaction for bosonic DM because of the Bose-enhanced reaction at very low momentum. By utilizing a simple $1 \leftrightarrow 2$ decay/inverse decay process to produce DM, I demonstrate that eV range bosonic DM can be thermally produced in a cold manner from a hot plasma. I also discuss some caveats arising from this phenomenon in the freeze-in production of DM, and present a related system that can suppress the hot plasma with thermal reaction.

会場: via Zoom

イベント公式言語: 英語

First X-ray polarimetry of neutron stars with strong magnetic fields

2023年9月25日(月) 13:30 - 15:00

玉川 徹 (理化学研究所 開拓研究本部 (CPR) 玉川高エネルギー宇宙物理研究室 主任研究員)

We launched the world's first highly sensitive X-ray polarimetry satellite, IXPE, in December 2021. IXPE began observations in January 2022 and detected significant X-polarization from objects in all categories. The IXPE observations have opened a new window in astrophysics. In this talk, I will introduce IXPE and present the results of X-ray polarimetry observations of neutron stars with strong magnetic fields (magnetars and neutron star binaries). The neutron star observations show results quite different from our prior expectations and await further theoretical interpretation.

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

Induced gravitational waves from inflaton oscillons

2023年9月22日(金) 14:00 - 15:30

カロイアン・ディミトロフ・ロザノフ (東京大学 カブリ数物連携宇宙研究機構 (Kavli IPMU) 特任研究員)

We present a new way to study cosmic inflation with gravitational waves. The gravitational signal is generated thanks to nonlinear structures in the inflaton field, called oscillons. This novel probe allows us to test models of inflation which are challenging to test with CMB experiments.

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