Seminar
1013 events
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Seminar
Selective inference for testing trees and edges in hierarchical clustering and phylogeny
December 9 (Thu) 10:00 - 11:00, 2021
Hidetoshi Shimodaira (Professor, Graduate School of Informatics, Kyoto University / Team Leader, Mathematical Statistics Team, RIKEN Center for Advanced Intelligence Project (AIP))
Bootstrap resampling is quite useful for computing “confidence values” or “p-values” of trees and edges. However, they are biased and may lead to false positives (too many wrong discoveries) or false negatives (too few correct discoveries) depending on the “curvature” of the boundary surface of a hypothesis region in the data space. In addition, we face the issue of selection bias because we tend to use the dataset twice for hypothesis selection and its evaluation. I will explain these two types of bias and show methods to adjust the confidence values.
Venue: via Zoom
Event Official Language: English
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Seminar
Generalized Bernoulli process and computation of proportional areas for Venn diagram
December 8 (Wed) 16:00 - 18:00, 2021
Ryosuke Iritani (Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
*For detailed information about the seminar, please refer to the email.
Venue: via Zoom
Event Official Language: English
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Seminar
The Conley index of topological dynamical systems
December 3 (Fri) 16:00 - 18:00, 2021
Yosuke Morita (Assistant Professor, Department of Mathematics, Kyoto University)
The study of topological dynamical systems, i.e. continuous self-homeomorphisms (or continuous flows) on topological spaces, is important in both pure mathematics and applications. To each isolated invariant subset of a topological dynamical system, we can assign an invariant called the Conley index, which is (roughly speaking) a based space that describes the dynamics around the isolated invariant subset. It is used not only in the study of topological dynamical systems themselves but also in Manolescu’s construction of the Seiberg-Witten-Floer homotopy type (a spectrum-valued (3+1)-dimensional TQFT). In this talk, I am planning to explain a new construction of Conley indices, which is entirely non-homotopical and uses only basic general topology. *Please contact Keita Mikami or Hiroyasu Miyazaki's mailing address to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English
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Seminar
Simulation-based inference for multi-type cortical circuits
November 29 (Mon) 13:30 - 15:00, 2021
Enrico Rinaldi (Research Fellow, Physics Department, University of Michigan, USA)
In many scientific fields, ranging from astrophysics to particle physics and neuroscience, simulators for dynamical systems generate a massive amount of data. One of the crucial tasks scientists are spending their precious time on is comparing observational data to the aforementioned simulations in order to infer physically relevant parameters and their uncertainties, based on the model embedded in the simulator. This poses a problem because the likelihood function for realistic simulations of complex physical systems is intractable. Simulation-based inference techniques attack this problem using machine learning tools and probabilistic programming. I will start with an overview of the problem and explain the general application of simulation-based inference methods. Then I will describe an application of the methods to a model of neurons in the visual cortex of mice."
Venue: via Zoom
Event Official Language: English
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Seminar
Self-adjointness from quantum-classical correspondence
November 26 (Fri) 16:00 - 18:00, 2021
Koichi Taira (Assistant Professor, College of Science and Engineering Department of Mathematical Sciences, Ritsumeikan University)
Self-adjointness is a fundamental property of a linear operator in quantum mechanics. In physics, a self-adjoint operator is usually defined to be an operator which is own adjoint. However, this definition is in fact not satisfactory since a self-adjoint operator in this definition does not always have nice properties such as the spectral decomposition. Hence, in mathematics, a kind of completeness is also assumed in the definition of a self-adjoint operator. Here a natural question is how to judge whether an operator is self-adjoint. It has been believed that self-adjointness is closely related to completeness of the classical dynamics for a long time although a complete description of such relations has not been given so far. I am planning to talk about how self-adjointness is important in mathematical physics. Moreover, I will explain relations between self-adjointness and classical dynamics by introducing some examples. *Please contact Keita Mikami or Hiroyasu Miyazaki's mailing address to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English
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Seminar
Imaging Theory of Optical Microscopy: Basic to Super Resolution
November 25 (Thu) 13:30 - 15:00, 2021
Ryosuke Oketani (Assistant Professor, Physical Chemistry, Department of Chemistry, Faculty of Sciences, Kyushu University)
Optical microscopy is one of the sophisticated techniques to manipulate light based on well-established theories, as well as a powerful tool to observe living micro-organisms. The developments are still ongoing to overcome their limitations in observation. Recently, the invention of several super-resolution techniques has overcome the limit in spatial resolution caused by the wave nature of light. In this presentation, I discuss the theories behind optical microscopy. My talk starts with basic wave optics to explain how a lens forms and magnifies an image in a conventional microscope. Then, I introduce laser scanning microscopy as an alternative form to the microscope. At last, as a recent development, I discuss several super-resolution techniques, which utilize interesting theory to improve spatial resolution.
Venue: via Zoom
Event Official Language: English
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Seminar
The graph removal lemma
November 19 (Fri) 16:00 - 18:00, 2021
Shinichiro Seki (Assistant Professor, Aoyama Gakuin University)
We have recently proved an extension of the Green-Tao theorem on arithmetic progressions to number fields, in collaboration with Kai, Mimura, Munemasa and Yoshino. (Kai gave a talk on this result in March.) There are several promising approaches in this area, including ergodic theory and Fourier analysis, but we used a combinatorial tool, the relative hypergraph removal lemma proved by Conlon, Fox and Zhao. In the first half of this talk, I will give a survey of Szemerédi's regularity lemma and the graph removal lemma, and explain how to extend the removal lemma to the case of (weighted) hypergraphs. In the second half of this talk, I will present Fox's result on a quantitative version of the graph removal, and discuss the prospects for future research. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English
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Seminar
Spatial structure in ecology: the effects of dispersal network structure on biodiversity pattern and stability in metacommunities
November 18 (Thu) 10:00 - 11:00, 2021
Yuka Suzuki (Okinawa Institute of Science and Technology Graduate University (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.
Venue: via Zoom
Event Official Language: English
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Seminar
Topological exchange statistics in one dimension
November 17 (Wed) 17:00 - 18:15, 2021
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Geometry in optical responses of quantum materials
November 15 (Mon) 13:30 - 15:00, 2021
Naoto Nagaosa (Deputy Director, Group Director, Strong Correlation Theory Research Group, RIKEN Center for Emergent Matter Science (CEMS) / Professor, Department of Applied Physics, Graduate School of Engineering, The University of Tokyo)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Confluence for the K-theoretic J-function
November 12 (Fri) 16:00 - 18:00, 2021
Todor Milanov (Associate Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Axions around rotating black holes
November 12 (Fri) 14:00 - 16:00, 2021
Hirotaka Yoshino (Institute of Cosmophysics, Department of Physics, Graduate School of Science, Kobe University)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Toward mathematical medicine: development of a new drug and digital medicine for sleep disorders
November 11 (Thu) 12:30 - 13:30, 2021
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Hunting hypernuclei by machine learning in nuclear emulsions
November 8 (Mon) 14:00 - 15:00, 2021
Takehiko Saito (Chief Scientist, High Energy Nuclear Physics Laboratory, RIKEN Cluster for Pioneering Research (CPR))
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.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
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Seminar
Geometry and Physics of Mirror Symmetry
November 5 (Fri) 16:00 - 18:00, 2021
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Boolean algebras and operator algebras
November 4 (Thu) 15:00 - 16:30, 2021
Michiya Mori (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Protein structure modeling from cryo-electron microscopy data
November 4 (Thu) 13:30 - 14:30, 2021
Takaharu Mori (Senior research scientist, Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research (CPR))
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Is the Standard Model in the Swampland? Consistency Requirements from Gravitational Scattering
November 2 (Tue) 14:30 - 16:00, 2021
Katsuki Aoki (Research Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
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.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
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Seminar
Nonlinear dynamics in frog choruses
October 28 (Thu) 10:00 - 11:00, 2021
Ikkyu Aihara (Associate Professor, Institute of Systems and Information Engineering, University of Tsukuba)
Male frogs produce sounds to attract conspecific females as well as advertise their own territories to other males. Subsequently male frogs acoustically interact with each other, which induces various types of synchronized behavior. In this seminar, I will introduce the synchronized calling behavior of actual male frogs as well as theoretical studies using a phase oscillator model [1, 2]. Next, I will introduce our recent projects on the identification of the phase oscillator model from empirical data [3] and the extension of the model to a hybrid dynamical system in which male frogs intermittently switch their behavioral mode based on internal condition and also the interaction with other males [4].
Venue: via Zoom
Event Official Language: English
1013 events