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399 イベント

セミナー
Introduction to instanton knot homology
2022年7月25日(月)16:00  18:00
井森 隼人 (京都大学 大学院理学研究科 数学・数理解析専攻 博士課程)
Floer theory is an infinitedimensional version of Morse theory and has provided powerful invariants in the study of lowdimensional topology. In the context of YangMills gauge theory, some versions of Floer homology groups for knots have been developed. These knot invariants are called instanton knot homology groups and are strongly related to representations of the fundamental group of the knot complement. In this talk, the speaker introduces basic constructions of instanton knot homology groups and recent developments related to the equivariant version of instanton knot homology theory.
会場: コモンルーム 246248号室 とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
Superconductinglike heat current: Effective cancellation of currentdissipation tradeoff by quantum coherence
2022年7月25日(月)13:30  15:00
田島 裕康 (電気通信大学 大学院情報理工学研究科 助教)
Recent developments in statistical mechanics have revealed a tradeoff between heat current and dissipation [1,2]. In various situations, this currentdissipation tradeoff represents a relationship between thermal energy flow and entropy increase, similar to Joule’s law W=RI^2. On the other hand, the coherence effect on the currentdissipation tradeoff has not been thoroughly analyzed. Here, we systematically analyze how coherence affects the currentdissipation tradeoff [3]. The results can be summarized in the following three rules:
会場: via Zoom
イベント公式言語: 英語

セミナー
Bayesian optimization of multivariate genomic prediction models based on secondary traits for improved accuracy gains and phenotyping costs
2022年7月21日(木)16:00  17:00
濱崎 甲資 (東京大学 大学院農学生命科学研究科 博士課程)
In recent years, the genomic prediction that predicts phenotypic values from marker genotype data has attracted much more attention in the area of breeding. Especially, genomic selection using prediction values based on genomic prediction models has been contributing to more efficient and rapid breeding. In genomic prediction, it is important to construct the prediction model so that its accuracy becomes higher. Thus, multivariate genomic prediction models with secondary traits, such as data from various omics technologies including highthroughput phenotyping (e.g., unmanned aerial vehiclebased remote sensing), have started to be applied to many datasets because it offers improved accuracy gains compared with genomic prediction based only on marker genotypes. Although there is a tradeoff between accuracy gains and phenotyping costs of secondary traits, no attempt has been made to optimize these tradeoffs. In this study, we propose a novel approach to optimize multivariate genomic prediction models with secondary traits measurable at early growth stages for improved accuracy gains and phenotyping costs. The proposed approach employs Bayesian optimization for efficient Pareto frontier estimation, representing the maximum accuracy at a given cost. The proposed approach successfully estimated the optimal secondary trait combinations across a range of costs while providing genomic predictions for only about 20% of all possible combinations. The simulation results reflecting the characteristics of each scenario of the simulated target traits showed that the obtained optimal combinations were reasonable. Analysis of realtime target trait data showed that the proposed multivariate genomic prediction model had significantly superior accuracy compared to the univariate genomic prediction model.
会場: via Zoom
イベント公式言語: 英語

SeibergWitten Floer homotopy
2022年7月15日(金)14:00  16:30
今野 北斗 (東京大学 大学院数理科学研究科 助教)
I will survey a mathematical object called the SeibergWitten Floer homotopy type introduced by Manolescu. This is a machinery that extracts interesting aspects of 3 and 4dimensional manifolds through the SeibergWitten equations. This framework assigns a 3manifold to a "space" (more precisely, the stable homotopy type of a space), and this space contains rich information that is strong enough to recover the monopole Floer homology of the 3manifold, which is known already as a strong invariant. I shall sketch how this theory is constructed along Manolescu's original work, and introduce major applications. If time permits, I will also explain recent developments of SeibergWitten Floer homotopy theory. If you are not familiar with the mathematical formulation of TQFT and categorification, I recommended you to watch Dr. Sano's recent talk in advance (see related links).
会場: コモンルーム 246248号室 とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
Dual stochasticity of neurons and synapses for samplingbased learning in the brain
2022年7月14日(木)16:00  17:00
寺前 順之介 (京都大学 大学院情報学研究科 先端数理科学専攻 非線形物理学講座 准教授)
Neurons and synapses behave highly stochastically in the brain. However, how this stochasticity is beneficial for computation and learning in the brain remains largely unknown. In this presentation, we will see that the stochastic processes in neurons and synapses can be integrated into a unified framework to optimally sample events from the environments, resulting in an efficient learning algorithm consistent with various experimental results. In particular, the learning algorithm enables us to reproduce the recently discovered efficient powerlaw coding in the cortex. These results suggest that synapses and neurons work cooperatively to implement a fundamental method for stochastic computing in the brain.
会場: via Zoom
イベント公式言語: 英語

Speed limits for macroscopic transitions
2022年7月13日(水)13:30  15:00
濱崎 立資 (理化学研究所 開拓研究本部 (CPR) 濱崎非平衡量子統計力学理研白眉研究チーム 理研白眉研究チームリーダー)
Speed of state transitions in macroscopic systems is a crucial concept for foundations of nonequilibrium statistical mechanics as well as various applications in quantum technology represented by optimal quantum control. While extensive studies have made efforts to obtain rigorous constraints on dynamical processes since Mandelstam and Tamm, speed limits that provide tight bounds for macroscopic transitions have remained elusive. Here, by employing the local conservation law of probability, the fundamental principle in physics, we develop a general framework for deriving qualitatively tighter speed limits for macroscopic systems than many conventional ones. We show for the first time that the speed of the expectation value of an observable defined on an arbitrary graph, which can describe general manybody systems, is bounded by the “gradient” of the observable, in contrast with conventional speed limits depending on the entire range of the observable. This framework enables us to derive novel quantum speed limits for macroscopic unitary dynamics. Unlike previous bounds, the speed limit decreases when the expectation value of the transition Hamiltonian increases; this intuitively describes a new tradeoff relation between time and the quantum phase difference. Our bound is dependent on instantaneous quantum states and thus can achieve the equality condition, which is conceptually distinct from the LiebRobinson bound. We also find that, beyond expectation values of macroscopic observables, the speed of macroscopic quantum coherence can be bounded from above by our general approach. The newly obtained bounds are verified in transport phenomena in particle systems and nonequilibrium dynamics in manybody spin systems. We also demonstrate that our strategy can be applied for finding new speed limits for macroscopic transitions in stochastic systems, including quantum ones, where the bounds are expressed by the entropy production rate. Our work elucidates novel speed limits on the basis of local conservation law, providing fundamental limits to various types of nonequilibrium quantum macroscopic phenomena.
会場: コモンルーム 246248号室 とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
Adiabatic pumps in quantum spin systems
2022年7月12日(火)16:00  17:15
塩崎 謙 (京都大学 基礎物理学研究所 助教)
The Thouless pump is a oneparameter cycle of 1dimensional gapped quantum systems with U(1) symmetry, which is classified by integers. In this talk, I introduce a generalization of the Thouless pump to quantum spin systems in any dimension with any finite group onsite symmetry. I show a simple model with Z_2 onsite symmetry, and how it is nontrivial via boundary degrees of freedom. Using the framework of the injective matrix product state, one can construct the topological invariant in a way similar to the Berry phase. If time allows, I will briefly introduce a group cohomology model by Roy and Harper for generic space dimensions and discuss its properties.
会場: via Zoom
イベント公式言語: 英語

セミナー
Stem cells determine complexity of hematopoiesis and immunity: A key in maintenance of homeostasis and fighting disease
2022年7月11日(月)10:00  11:30
石川 文彦 (理化学研究所 生命医科学研究センター (IMS) ヒト疾患モデル研究チーム チームリーダー)
The hematopoietic system, is a complex organ in which all cells, including white blood cells (also known as leukocytes), red blood cells and platelets originate from the hematopoietic stem cells. White blood cells/leukocytes are critical effectors of immunity. At baseline, we have about 500010000/microL circulating white blood cells/leukocytes, composed of more than ten distinct subsets. Among them, the most abundant (5060%) is the neutrophil, which are capable of preventing bacterial and fungal infection. Others include T lymphocytes which attack tumors and virusinfected cells and B lymphocytes that produce immunoglobulins. Each of the leukocyte subsets have different roles in protecting us from diseases. Defects in white blood cell number or function expose us to risks of infections and tumors. Maintenance of normal homeostasis of these white blood cells is governed by expression levels of approximately 20,000 genes in hematopoietic stem cells. In this presentation, first, I will discuss current understanding of a hierarchical system of stem cells generating many different kinds of leukocytes. Second, I will talk about leukemia, a cancer of white blood cells, in which critical genes are hit by mutations, resulting in a loss or gain of function of those genes in stem cells. Third, I would like to discuss with the iTHEMS scientists potential approaches by which we can collaborate to understand the normal and diseased human blood/immune systems.
会場: コモンルーム 246248号室 とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
Virus vs. Bacteria: Art of the war in the microbial world
2022年7月7日(木)16:00  17:00
御手洗 菜美子 (Associate Professor, Niels Bohr Institute, University of Copenhagen, Denmark)
A virulent phage (virus that infects bacteria) infection to a host bacterial cell results in lysis of the cell, where possibly hundreds of phage particles are released after a latency time. The phage pressure is believed to be an important factor to shape the microbial communities and a driving force of their evolution, and yet we are far from having a full picture of their warfare. In this talk, I highlight a few factors that play significant roles in phagebacteria interactions and their coexistence, such as the effect of herd immunity and the importance of the spatial structure in a few cells scale to the colony scale. *Her talk will be accessible to physicists, mathematicians, and also biologists.
会場: via Zoom
イベント公式言語: 英語

セミナー
Gradient flow exact renormalization group 2
2022年7月6日(水)13:30  17:00
鈴木 博 (九州大学 大学院理学研究院 教授)
Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has however been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Here, we propose a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gaugecovariant diffusion equation. I explain the basic idea and properties of GFERG. If time permits, I want to present a possible application of GFERG to the consideration of the axial anomaly.
会場: via Zoom
イベント公式言語: 英語

セミナー
Gradient flow exact renormalization group 1
2022年7月5日(火)13:30  17:00
鈴木 博 (九州大学 大学院理学研究院 教授)
Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has however been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Here, we propose a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gaugecovariant diffusion equation. I explain the basic idea and properties of GFERG. If time permits, I want to present a possible application of GFERG to the consideration of the axial anomaly.
会場: via Zoom
イベント公式言語: 英語

セミナー
Longterm evolution of a supernova remnant hosting a double neutron star binary
2022年7月1日(金)14:00  15:00
松岡 知紀 (京都大学 大学院理学研究科 博士課程)
Stellar mass loss is one of the crucial elements which determine the fate of progenitors of corecollapse supernovae (SNe). Since the material released from the progenitor will be distributed as circumstellar medium (CSM), it can also have an influence on the subsequent evolution of the SN or supernova remnant (SNR). Despite its importance, mass loss histories predicted by stellar evolution models have not been incorporated with modeling for SNRs. As a first step, we investigate the dynamical evolution of an ultrastripped supernova remnant (USSNR), originated from a type of corecollapse SN explosion proposed to be a candidate formation site of a double neutron star binary. By accounting for the massloss history of the progenitor binary using a model developed by a previous study, we construct the largescale structure of the CSM up to a radius ∼100 pc, and simulate the explosion and subsequent evolution of a USSN surrounded by such a CSM environment. We find that the CSM encompasses an extended region characterized by a hot plasma with a temperature ∼10^8 K located around the termination shock of the wind from the progenitor binary (∼10 pc), and the USSNR blast wave is drastically weakened while penetrating through this hot plasma. Radio continuum emission from a young USSNR is sufficiently bright to be detectable if it inhabits our galaxy but faint compared to the observed Galactic SNRs. In this seminar I will talk about the background of the connection between the models for stellar evolution and SNRs, the details of our methods, and future prospects.
会場: via Zoom
イベント公式言語: 英語

セミナー
Topological quantum effects in lowdimensional spin systems  The power of the boundary
2022年6月30日(木)17:00  18:15
Dr. Thore Posske (Group Leader, I. Institute for Theoretical Physics, University of Hamburg, Germany)
Manipulating the boundary of lowdimensional magnetic structures could grant control about topological magnetic quantum sates. I will discuss the creation of one and twodimensional topological quantum magnets by manipulating the boundary magnetization, address their stability against external perturbations, and discuss their possible application to quantum information processing.
会場: via Zoom
イベント公式言語: 英語

セミナー
Predicting local patterns of diversity: coexistence models, networks and wildflowers
2022年6月30日(木)10:00  11:30
Dr. Margie Mayfield (Professor, University of Melbourne, Australia)
The question of how species coexist in diverse natural communities has challenged ecologists for generations. Theoretical models of species coexistence have been developed, but primarily as proof of concept for specific coexistence theories. These theories and associated models focus on coexistence between species pairs and ignore the great complexity of interactions found in most natural systems. Though useful for advancing ecological theory, these models are often of limited use for understanding and predicting diversity in real natural communities. In this talk, I explore the three main assumptions made by coexistence models developed under the framework of Modern Coexistence Theory (MCT): that only direct competition is important, that demographic variation is noise, not valuable biological information, and that only the average environment matters. Using Bayesian statistical approaches with population growth models applied to field data from the annual plant communities of the York gum woodlands of SW Western Australia, I illustrate the issues with these assumptions in predicting coexistence in diverse systems. I show how these Bayesian approaches to MCT can improve on frequentist approaches and discuss the potential value of interaction networks for studying coexistence dynamics in diverse natural systems.
会場: 大河内記念ホール (メイン会場) / via Zoom
イベント公式言語: 英語

Mathematical modeling of understanding how adaptive evolution of sexual traits can affect coexistence
2022年6月23日(木)16:00  17:00
森田 慶一 (総合研究⼤学院⼤学 先導科学研究科 生命共生体進化学専攻 博士課程)
One of the challenges in ecology is understanding the processes of species coexistence. Recent studies have underlined the importance of the interaction between rapid adaptation and population dynamics (i.e., ecoevolutionary feedbacks) in coexistence. Reproductive interference may reduce population growth rate due to costs of hybridization by incomplete recognition of sexual traits such as ornaments and songs in birds. Recent theoretical studies have suggested that ecoevolutionary feedbacks in sexual traits can affect coexistence. I will present mathematical modeling for investigating how reproductive interference can affect coexistence. Furthermore, I will present an analytical method, adaptive dynamics for understanding how evolution of sexual traits can affect coexistence.
会場: via Zoom
イベント公式言語: 英語

セミナー
Dress code for infrared safe Smatrix in QED
2022年6月22日(水)13:30  15:00
杉下 宗太郎 (名古屋大学 高等研究院 (IAR) 特任助教)
We consider the infrared (IR) aspects of the gauge invariant Smatrix in QED. I will review the problem of IR divergences in QED, and introduce the dressed state formalism to obtain IRsafe Smatrix elements. I will show a condition for dressed states to obtain IRsafe Smatrix elements, and explain that this condition can be interpreted as the memory effect and is related to asymptotic symmetry. I also explain that IR divergences are necessary to prohibit the violation of asymptotic symmetry. We also argue that the difference between dressed and undressed states can be observed, even if we are able to observe an inclusive crosssection summing over soft photons.
会場: コモンルーム 246248号室 とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
Topological aspects of nonHermitian physics
2022年6月21日(火)16:00  17:15
大熊 信之 (京都大学 基礎物理学研究所 助教)
The past decades have witnessed an explosion of interest in topological materials, and a lot of mathematical concepts have been introduced in condensed matter physics. Among them, the bulkboundary correspondence is the central topic in topological physics, which has inspired researchers to focus on boundary physics. Recently, the concepts of topological phases have been extended to nonHermitian Hamiltonians, whose eigenvalues can be complex. Besides the topology, nonHermiticity can also cause a boundary phenomenon called the nonHermitian skin effect, which is an extreme sensitivity of the spectrum to the boundary condition. In this talk, I will explain recent developments in nonHermitian topological physics by focusing mainly on the boundary problem. As well as the competition between nonHermitian and topological boundary phenomena, I will discuss the topological nature inherent in nonHermiticity itself. Field: condensed matter physics Keywords: topological materials, nonHermitian systems, skin effect, bulkboundary correspondence
会場: via Zoom
イベント公式言語: 英語

セミナー
Selforganisation of a dynamic meshwork structure in the mesoderm during the development of a chick embryo and its characterisation using persistent homology
2022年6月16日(木)16:00  17:00
多羅間 充輔 (理化学研究所 生命機能科学研究センター (BDR) フィジカルバイオロジー研究チーム 研究員)
Morphogenesis is a fundamental process of development. Appropriate morphogenesis of tissues is achieved by coordinated motion of individual cells. To elucidate the mechanism behind this selforganisation of cells, one needs to develop a theoretical model based on experimental observations. In our recent study, our experimental colleague found that the mesoderm cells in early chick embryo organise into a meshwork structure, which changes dynamically. To understand the mechanism behind this dynamic meshwork structure formation, we developed an agentbased mechanical model of cells that interact through a shortrange attractive interaction. To compare the simulation results with the experiment, we utilized persistent homology, a method of topological data analysis that allows to systematically characterise irregular structures. In this seminar, we will talk about the mechanical mechanism behind the mesoderm structure formation during the development of the early chick embryo, and how the persistent homology analysis is applied to our biological system.
会場: via Zoom
イベント公式言語: 英語

セミナー
Implications of singularity theorem for nonsingular universe
2022年6月16日(木)13:30  15:00
吉田 大介 (名古屋大学 大学院多元数理科学研究科 特任助教)
The singularity theorem by Penrose shows that a spacetime singularity arises in certain universal situations. The existence of a spacetime singularity is thought to represent a breakdown in the validity of theories such as general relativity and the phenomenological models of the universe. Thus, if we could build a correct model that describes the beginning of the universe, the universe predicted by that model should be nonsingular. In this talk, we will discuss general properties that a nonsingular universe must satisfy in order to avoid the singularity theorem. In particular, we will see that the universe must be, in some sense, smaller than the corresponding closed de Sitter spacetime.
会場: コモンルーム 246248号室 とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
NonAbelian vortices in twoflavor dense QCD
2022年6月15日(水)13:30  15:00
藤本 悠輝 (Postdoctoral Scholars, Department of Physics, University of Washington, USA)
Recently, the phase of the twoflavor quark matter with the new pattern of color superconductivity was proposed so that the continuous crossover from the hadronic to the quark phase is realized [1]; it is in consonance with the recent observation of neutron stars. In this talk, I will show the classification of the topological vortices in this phase. We found that the stable vortices are what we call the "nonAbelian Alice strings" [2]. They are superfluid vortices carrying 1/3 quantized circulation and color magnetic fluxes. I will discuss their properties in comparison to the wellestablished CFL vortices in threeflavor symmetric setup, by putting some emphasis on their peculiarity: the nonAbelian generalization of the Alice property. I will then discuss in detail the possibility that these vortices are confined as well as how the vortices in the quark phase can be connected to those in the hadronic phase [3]. [1] Y. Fujimoto, K. Fukushima, W. Weise, PRD 101, 094009 (2020) [1908.09360]. [2] Y. Fujimoto, M. Nitta, PRD 103, 054002 (2021) [2011.09947]; JHEP 09 (2021) 192 [2103.15185]. [3] Y. Fujimoto, M. Nitta, PRD 103, 114003 (2021) [2102.12928].
会場: via Zoom
イベント公式言語: 英語
399 イベント
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