セミナー
709 イベント
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セミナー
Spatial structure in ecology: the effects of dispersal network structure on biodiversity pattern and stability in metacommunities
2021年11月18日(木) 10:00 - 11:00
鈴木 裕香 (沖縄科学技術大学院大学 (OIST))
Ecological dynamics typically take place at a large spatial scale. However, it has been challenging to study them at a scale as large as a country, continent, or ocean. In particular, while there are many studies that consider systems with multiple local patches (known as "metacommunities"), spatial structures assumed in these studies are mostly simple or focused on a particular structure, despite the diverse landscape structures seen in nature. Thus, to understand how spatial structures affect metacommunities in nature, we need to expand our understanding of the role of spatial structure in regulating biodiversity patterns and stability across diverse spatial structures. In my study, I addressed this issue by using computer simulation with theoretical and empirical spatial structures. In this talk, I will show how the use of computational tools and network theoretical concepts aided investigating unexplored aspects of spatial structure and dissecting the complex nature of spatial network structure. Results suggest that how dispersal pathways are distributed in the network space affects total diversity, and the number of patches in a metacommunity is the dominant spatial parameter that regulate stability. Such an improved understanding of the role of spatial structure could contribute to a better conservation planning as well.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Topological exchange statistics in one dimension
2021年11月17日(水) 17:00 - 18:15
Harshman Nathan (Department of Physics, American University, USA)
In two dimensions, the topological approach to exchange statistics predicts the existence of anyons obeying statistics given by the braid group. However, in one dimension the topological approach is ambiguous because particles cannot exchange without coincidence and scattering. I will review the topological approach and show how old controversies can be resolved using orbifolds (roughly, manifolds with symmetry) to describe configuration space for one-dimensional systems. Using orbifolds also predicts new topological physics, including possibilities for “traid group” statistics when there are three-body interactions in one dimension and non-abelian statistics for indistinguishable particles on a ring. *Detailed information about the seminar refer to the email.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Geometry in optical responses of quantum materials
2021年11月15日(月) 13:30 - 15:00
永長 直人 (理化学研究所 創発物性科学研究センター (CEMS) 強相関理論研究グループ 副センター長, グループディレクター / 東京大学 大学院工学系研究科 物理工学専攻 教授)
Studies on optical responses of solids have the long history, and has been considered to be well established. However, a new development has been on-going recently, which explores the geometric nature of the electronic states in solids and its crucial role in optical processes. In this talk, I discuss the geometry and topology in the optical responses both in linear and nonlinear regimes, which includes (i) optical responses in clean superconductors, (ii) shift current in noncentrosymmetric quantum materials driven by Berry phases, and (iii) Riemannian geometry in nonlinear optical responses.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Confluence for the K-theoretic J-function
2021年11月12日(金) 16:00 - 18:00
Todor Milanov (東京大学 カブリ数物連携宇宙研究機構 (Kavli IPMU) 准教授)
I am planning to talk about my recent paper (1) written in collaboration with Alexis Roquefeuil. In the first part of the talk I would like to explain the background of our project: quantum differential equations and K-theoretic quantum q-difference equations in genus-0 Gromov--Witten theory. In the second part of the talk, I would like to explain our main result with an interesting application. Namely, under the assumption that the first Chern class of the tangent bundle is positive, we proved that the small J-function in quantum cohomology can be obtained as a limit q -->1 of the small J-function in quantum K-theory. In the case of a Fano toric manifold of Picard rank 2, we proved the K-theoretic version of an identity due to Iritani that relates the I-function of the toric manifold and the oscillatory integral of the toric mirror. In particular, our confluence result yields a new proof of Iritani's identity in the case of a Fano toric manifold of Picard rank 2. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Axions around rotating black holes
2021年11月12日(金) 14:00 - 16:00
吉野 裕高 (神戸大学 大学院理学研究科 物理学専攻 宇宙論研究室)
String theories indicate the existence of many axionlike scalar fields with light masses in addition to the QCD axion. If this is the case, an axion field around a rotating black hole extracts the energy of the black hole by the mechanism called the “superradiant instability”. Then, every astrophysical black hole is expected to wear a cloud of the axion. In this talk, I would like to give an overview on this topic, and introduce our numerical studies on the phenomena caused by the axion cloud at the last stage of the superradiant instability where the self-interaction of axions becomes important.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Toward mathematical medicine: development of a new drug and digital medicine for sleep disorders
2021年11月11日(木) 12:30 - 13:30
Jae Kyoung Kim (Associate Professor, Department of Mathematical Sciences, KAIST, Republic of Korea)
In this talk, I will illustrate collaborative stories between our math group and medical researchers to treat disrupted circadian rhythms and sleep. First, I will illustrate the key molecular mechanism for robust circadian rhythms against spatio-temporal noise, which we identified by analyzing spatio-temporal timeseries data of clock molecules. This explains why Alzheimer's diseases, obesity, and aging cause unstable circadian rhythms and sleep-wake cycle: cytoplasmic traffic jam, which provides a new paradigm to treat sleep disorders. Next, I will talk about our collaboration story with Pfizer Inc: how we used mathematical modeling to help the development of a new drug modulating the circadian phase. Finally, I will introduce our collaboration with Samsung medical center: how we used mathematical modeling to analyze complex sleep patterns of shift workers measured with wearables to find optimal sleep patterns minimizing sleep disorders. This opens the chance for the development of an app providing a personalized sleep schedule for shift workers.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Hunting hypernuclei by machine learning in nuclear emulsions
2021年11月8日(月) 14:00 - 15:00
齋藤 武彦 (理化学研究所 開拓研究本部 (CPR) 齋藤高エネルギー原子核研究室 主任研究員)
A hypernuclus is a subatomic systems with strange quark(s). They have been studied already for seven decades for understanding the fundamental baryonic interaction and nuclear matters inside the core of neutron stars. The hypertriton is the lightest hypernucleus with a neutron, a proton and a Lambda hyperon, and it is the benchmark in hypernuclear studies. However, recent experimental studies with heavy ion beams have revealed that the nature of the hypertriton is unclear, especially on its biding energy and lifetime. The most urgent issue is to measure its binding energy very precisely. Measurements with nuclear emulsion have provided the best precision for the hypernuclear binding energy, however, it requires a huge human load on visual image analyses. We have developed machine learning models to detect events associated with production and decay of hypertriton in nuclear emulsions data, and we have already discovered hypertriton events [1]. In the seminar, we’ll discuss the challenges and developments of our machine learning models as well as the outcomes and perspectives of our works.
会場: コモンルーム 246-248号室 とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Geometry and Physics of Mirror Symmetry
2021年11月5日(金) 16:00 - 18:00
Naichung Conan Leung (Professor of Mathematics, Department of Mathematics, The Institute of Mathematical Sciences, The Chinese University of Hong Kong, Hong Kong)
In the first half of this talk, I will describe the geometry and physics behind mirror symmetry in layman's terms. In the second half of this talk, I will provide a more mathematical explanation of the concepts involved in this mysterious conjecture. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Boolean algebras and operator algebras
2021年11月4日(木) 15:00 - 16:30
森 迪也 (数理創造プログラム 基礎科学特別研究員)
The concept of Boolean algebra was introduced by George Boole in 1847. It plays a fundamental role in the theory of propositional logic. The theory of operator algebras was initiated by John von Neumann in around 1930. A keyword of the latter theory is "noncommutativity". In this talk, I will first explain basics of Boolean algebras and some ideas in operator algebra theory. Then I will talk about my recent attempt to give a new formulation of the concept of "noncommutative Boolean algebras" in an operator algebraic framework.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Protein structure modeling from cryo-electron microscopy data
2021年11月4日(木) 13:30 - 14:30
森 貴治 (理化学研究所 開拓研究本部 (CPR) 杉田理論分子科学研究室 専任研究員)
Recent advances in cryo-electron microscopy (cryo-EM) have enabled us to determine three-dimensional structures of biomolecules at near-atomic resolution. Protein structure modeling from experimental cryo-EM data can be achieved using a molecular dynamics (MD) simulation, called flexible fitting. We have developed MD-based flexible fitting algorithms for efficient and reliable protein structure modeling. In this seminar, I would like to talk about our recent contributions to this field, and propose perspectives towards next-generation structural biology.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Is the Standard Model in the Swampland? Consistency Requirements from Gravitational Scattering
2021年11月2日(火) 14:30 - 16:00
青木 勝輝 (京都大学 基礎物理学研究所 基研特任助教)
Underlying assumptions on ultraviolet completion can impose constraints on its low-energy effective field theories (EFTs). The swampland program aims to clarify consistent and inconsistent EFTs with quantum gravity and aims to understand quantum gravity from low-energy physics and vice versa. One of the most well-established constraints is called positivity bounds, provided that general assumptions such as Poincare invariance and unitarity are satisfied at all scales. I will first explain how these consistency conditions arise especially in the presence of gravity. I will then show that the positivity bound is violated if the Standard Model of particle physics coupled to General Relativity is extrapolated up to 10^16 GeV, requiring new physics there or below. The precise value of the cutoff is determined by hadronic physic while it is insensitive from non-gravitational physics beyond the Standard Model. This is a signal from established physics for the necessity of quantum gravity below 10^16 GeV.
会場: コモンルーム 246-248号室 とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Nonlinear dynamics in frog choruses
2021年10月28日(木) 10:00 - 11:00
合原 一究 (筑波大学 システム情報系 准教授)
カエルのオスは、同種のメスを惹き寄せたり同種のオスへの縄張りを主張すべく鳴きます。結果としてオスは互いに相互作用しますが、そのなかにはさまざまな同調現象があります。この講演では、演者はオスの実際の同調的な鳴き方を紹介しつつ、その位相振動子モデルを紹介します[1,2]。続いて、最近取り組んでいるプロジェクトである、実証データから位相振動子を同定する研究を紹介します[3]。そしてモデルをハイブリッド力学系に拡張し、内在的な条件や同種オスとのやりとりに応じて オスが断続的に鳴き方を変更する現象の研究を紹介します[4]。
会場: via Zoom
イベント公式言語: 英語
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セミナー
Geometry of hyperkahler 4 manifolds
2021年10月22日(金) 13:00 - 15:00
Song Sun (Associate Professor, Department of Mathematics, University of California, Berkeley, USA)
An n dimensional Riemannian metric g defines a holonomy group, which is a subgroup of SO(n) given by parallel transport along all contractible loops (with respect to the Levi-Civita connection). According to the Berger classification we know that if a complete Riemannian metric is not locally symmetric and not locally reducible then its holonomy group is either the entire SO(n) (generic case), or U(n) (Kahler), or is special and belongs to a small list. Riemannian metrics with special holonomy are very interesting geometric objects to study, with many connections to analysis and physics. The simplest model is given by a 4 dimensional hyperkahler metric. We will explain the general background and discuss recent progress on understanding the geometry of hyperkahler 4 manifolds. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Evaluation of origin of driving force for loop formation in a chromatin fiber
2021年10月21日(木) 10:00 - 11:00
横田 宏 (数理創造プログラム 特別研究員)
During cell division, chromatin fiber is condensed into the rod-like shape which is called chromosome. The rod-like shape of the chromosome is constructed by consecutive chromatin loop structures which are formed by the protein complex named condensin. In this talk, by calculating the driving force for the loop formation, we discuss the mechanism of loop formation which is the one of the controversial issues on chromosome condensation. The driving force is evaluated based on the free energy of the chromatin loop formation by constructing the polymer model. Based on the free energy, the loop growth length in the unit time is also evaluated. These evaluations also lead to the time evolution of the loop length and the mechanism of the loop formation.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Nonlinear response in strongly correlated systems
2021年10月20日(水) 17:00 - 18:15
Robert Peters (京都大学 大学院理学研究科 講師)
Nonlinear responses in condensed matter are intensively studied because they provide rich information about materials and hold the possibility of being applied in diodes or high-frequency optical devices [1-4]. While nonlinear responses in noninteracting models have been explored widely, the effect of strong correlations on the nonlinear response is still poorly understood. This talk will introduce a Green's function method to calculate nonlinear conductivities in strongly correlated materials [5-6]. Correlation effects are thereby included by the self-energy of the material. I will then use this method to study the nonlinear conductivities in noncentrosymmetric f-electron systems. The first system is a heavy Fermion system, where a nonreciprocal conductivity appears in the ferromagnetic phase. The nonreciprocal conductivity thereby always occurs perpendicular to the magnetization of the system and has a strong spin dependence, which might be advantageous for spintronic applications. The second system is a model corresponding to the Weyl-Kondo semimetal Ce3Bi4Pd3, in which a giant spontaneous Hall effect without time-reversal symmetry breaking has been observed [7]. This Hall effect can be explained as a nonlinear Hall effect in an inversion-symmetry broken Weyl-semimetal. It has been shown that the nonlinear Hall effect is related to the Berry curvature dipole [4]. Our study shows that the magnitude of the experimentally observed nonlinear Hall effect can be explained by the strong correlations inherent in this f-electron material [8]. *Detailed information about the seminar refer to the email.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Floquet vacuum engineering: laser-driven chiral soliton lattice in the QCD vacuum
2021年10月20日(水) 13:30 - 15:00
山田 晃弘 (慶應義塾大学 大学院理工学研究科 基礎理工学専攻 修士課程)
What happens to the QCD vacuum when a time-periodic circularly polarized laser field with a sufficiently large intensity and frequency is applied? Based on the Floquet formalism for periodically driven systems and the systematic low-energy effective theory of QCD, we show that for a sufficiently large frequency and above a critical intensity, the QCD vacuum is unstable against the chiral soliton lattice of pions, a crystalline structure of topological solitons that spontaneously breaks parity and continuous translational symmetries. In the chiral limit, in particular, the QCD vacuum is found unstable by the laser with an arbitrary small intensity. Our work would pave the way for novel “Floquet vacuum engineering.”
会場: via Zoom
イベント公式言語: 英語
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セミナー
Distinctive signals of boosted dark matter from semi-annihilations
2021年10月20日(水) 10:00 - 11:30
藤間 崇 (金沢大学 国際基幹教育院 GS教育系 助教)
The recent dark matter direct detection experiments impose the stringent upper bound on the elastic scattering cross section with nucleons. This implies that the cross section is suppressed by small dark matter velocity. However such dark matter can be probed if it is boosted by some mechanism. In this talk, we show that the specific semi-annihilation channel where two dark matter particles annihilate into a pair of anti-dark matter and neutrino indicates signals distinctive from the other semi-annihilation and standard dark matter annihilation processes. Since the boosted dark matter produced by this semi-annihilation is regarded as a high energy neutrino, the total flux of the dark matter and the accompanying neutrino yields double peaks at the energy close to the dark matter mass. Both of the particles can be detectable at large volume neutrino detectors.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Recent progress on the r-process in the era of gravitational-wave astronomy
2021年10月15日(金) 16:00 - 18:00
西村 信哉 (理化学研究所 開拓研究本部 (CPR) 長瀧天体ビッグバン研究室)
The r-process, the rapid neutron-capture process, is a major origin of heavy nuclei beyond iron in the universe, occurring in explosive astrophysical phenomena with very neutron-rich environments. In the studies of r-process nucleosynthesis, there are several unsolved problems in nuclear physics and astrophysics. In this talk, I will briefly summarize recent progress on the studies of the r-process, mainly focusing on neutron star mergers. We will see that the scenario of neutron star mergers is consistent with several observations, e.g., GW170817 with a kilonova, chemical evolution of r-process elements. In addition, nevertheless, there are several remaining (or newly realized) problems on the origin of r-process elements in the universe. Focusing on our own research, I will introduce attempts to address these issues.
会場: via Zoom
イベント公式言語: 英語
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セミナー
The branched deformations of special Lagrangian submanifolds
2021年10月15日(金) 10:00 - 12:00
Siqi He (Research Assistant Professor, Simons Center for Geometry and Physics, Stony Brook University, USA)
Special Lagrangian submanifolds are a distinguished class of real calibrated submanifolds defined in a Calabi-Yau manifold, which are calibrated by the real part of the holomorphic volume form. Given a compact, smooth special Lagrangian submanifold, Mclean proved that the space of nearby special Lagrangian submanifolds of it could be parametrized by the harmonic 1-forms. In this talk, we will discuss some recent progress on generalizing Mclean’s result to the branched deformations. We will describe how to use multi-valued harmonic functions to construct branched nearby deformations. In the first one hour, we will introduce the background of special Lagrangian submanifold and explain the motivations to study this problem. In this second one hour, we will discuss the technical details and interesting new phenomenon in this branching deformation problem. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.
会場: via Zoom
イベント公式言語: 英語
709 イベント