セミナーレポート
325 ニュース
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2022-09-05
セミナーレポート
iTHEMS-RNC Meson Science Lab. Joint Seminar by Dr. Natsuki Tomida on August 26, 2022
Natsuki Tomida (SACRA, Kyoto Univ.) gave a hybrid talk on her experimental research on the bound eta'-meson in nuclei. This is related to the topic "Mesons in Nuclei" which is one of the central subjects in modern hadron physics. Both experimentalists and theorists from Nishina Center and iTHEMS joined the seminar, and there was a hot discussion on this interesting topic. Natsuki joined iTHEMS on Aug.1, 2022 as a visiting scientist to promote collaboration between SACRA's MACS program at Kyoto Univ. and RIKEN iTHEMS. On Sept. 20-21, 2022, she will visit iTHEMS again together with 11 undergraduate and graduate students of Kyoto University. Reported by Tetsuo Hatsuda
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2022-09-02
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iTHEMS Biology Seminar by Dr. Hiroshi Yokota on September 1, 2022
In the iTHEMS biology seminar on September 1st, I, Hiroshi Yokota, talked about a theoretical model of chromosome condensation based on Langevin simulation. In this model, the twist and the writhe structures on biopolymer is quantified in a computational manner. In this seminar, I enjoyed the discussion with audiences on the computational method and the definition of the twist and the writhe. Thank you so much! Reported by Hiroshi Yokota
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2022-08-26
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ABBL-iTHEMS Joint Astro Seminar by Dr. Yosuke Mizuno on August 26, 2022
Dr. Yosuke Mizuno presented the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength 1.3 mm. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of ~50 micro-arcsecond. Using a large suite of numerical simulations, The EHT group demonstrated that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 million solar mass, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Their model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50 deg), as well as non-spinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way. In the seminar, Dr. Yosuke Mizuno focused on more theoretical interpretation and model comparison to understand the accretion flow properties nearby Sgr A*. Reported by Shigehiro Nagataki
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2022-08-08
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iTHEMS Math Seminar by Prof. Narutaka Ozawa on August 2, 2022
On August 2, Professor Narutaka Ozawa (RIMS, Kyoto University) gave a talk entitled "Product Replacement Algorithm, Semidefinite Programming, and Operator Algebras" in the iTHEMS Math Seminar. He elegantly explained how his recent study on Kazhdan's property (T) ties the field of functional analysis/operator algebras and that of computer sciences. Reported by Michiya Mori
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2022-08-05
セミナーレポート
iTHEMS Math Seminar by Dr. Hokuto Konno on July 15, 2022
On July 15, there was a math seminar by Professor Konno. He gave an introductory talk on the Seiberg-Witten Floer homotopy type. Reported by Keita Mikami
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2022-08-04
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Seminar by Dr. Xavier Roca-Maza on August 3, 2022
As a part of the RCNP domestic workshop on low-energy nuclear physics and high-energy astrophysics (RCNP研究会「低エネルギー核物理と高エネルギー天文学で読み解く中性子星」), the special seminar entitled "How does subatomic matter organize itself? A low-energy nuclear physics perspective" was given by Prof. Xavier Roca-Maza in U. Milan. This seminar is supported by Gravitational Wave and Equation of State Working Group (GW-EOS WG), RIKEN iTHEMS Program. The equation of state (EoS) of nuclear matter is one of the essential things in nuclear physics. There have been many attempts to determine parameters characterizing the EoS experimentally, which have become paid attention more. He introduced various attempts and theoretical mechanisms, including cutting-edge proposals. More than 80 participants attended the seminar, including from the foreign country. Reported by Tomoya Naito
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2022-07-29
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iTHEMS Colloquium by Prof. Yasunori Nomura on July 26, 2022
Prof. Yasunori Nomura, the director of the Berkeley Center for Theoretical Physics, the University of California, Berkeley, visited iTHEMS and gave a colloquium entitled “From the Black Hole Conundrum to the Structure of Quantum Gravity” on July 26th. Prof. Nomura started the colloquium by explaining that the two pillars of modern physics, quantum mechanics and general relativity are actually at odds with each other, but each of them usually governs a different domain of physical phenomena, thus obscuring the incompatibility. The focus of the colloquium lies on one of the areas where both quantum mechanics and general relativity become equally important, namely quantum theory of black holes. Prof. Nomura illustrated how the famous phenomenon of black holes discovered by Stephen Hawking, Hawking radiation leads to so-called information paradox, in which the conservation the probability appears to be violated during the process of the radiation from the horizon. He went on to describe the key ingredients in solving the paradox, which are the concept of holography, the stretched horizon, and AdS/CFT correspondence. In the latter part of the colloquium, Prof. Nomura pedagogically showed the audience the most recent development in the study of the information paradox. The calculation including the contribution from “wormholes” was shown to reproduce the Page curve implying the recovery of the lost probability. The same calculation was also explained through formalism which was developed by Prof. Nomura himself. He concluded with the message that the study of the black hole conundrum is thus revealing the structure of quantum gravity, which involves with a wide range of various research fields such as high energy physics and astrophysics, quantum information science, and many-body physics. The colloquium was taken place at the 2F Large Meeting Room of RIBF Building and was attended by a limited number of audience in person due to the wide spreading of COVID-19, but more than eighty people joined through zoom. Reported by Tsukasa Tada
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2022-07-25
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iTHEMS Biology Seminar by Dr. Namiko Mitarai on July 7, 2022
Dr. Namiko Mitarai (Niels Bohr Institute) gave us an amazing talk in the biology seminar. She told us about the collaborative works with experimental biologists on a microbial world. Some viruses that infect bacteria are known to provide immunity to infection by the same virus. According to her, no-immune bacteria can be protected from infection when the ratio of immune bacteria is substantially high in the population, which reminds us of our current cases for Covid-19. Interestingly, the metabolic state of host (bacteria) also affects the virus infection. The talk was very very exciting. In the end of her seminar, she also showed us the tips for the successful collaboration with experimental biologists: (1) We (theorists) should care about them. (2) They (experimental biologists) should care about us. During and after the talk, there were lively discussion between the speaker and iTHEMS researchers. Thanks Mitarai-san!! Reported by Gen Kurosawa
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2022-07-15
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iTHEMS Biology Seminar by Dr. Jun-nosuke Teramae on July 14, 2022
In this week’s biology seminar, we were very happy to have Dr. Jun-nosuke Teramae from Kyoto University to tell us about the mysterious stochastic behavior of neurons and synapses in the brain. Many biological experimental observations are reported. However, how this stochasticity is beneficial for computation and learning in the brain remains largely unknown. Dr. Teramae presented his work on developing an efficient learning algorithm inspired by this brain behavior. The algorithm is based on Gibbs-sampling which allow us to efficiently obtain high-dimensional sampling results. The algorithm shows similar stochastic behavior of the brain, which other machine leaning algorithms doesn’t show. In the end, Dr. Teramae briefly showed us the algorithm enables us to reproduce the recently discovered efficient power-law coding in the cortex. Even the seminar time is ended, the discussion continued for a long while. The seminar inspired many open questions on brain behavior and learning algorithms, both for the speaker and the audiences. We look forward to further development on the subjects. We thank Dr. Jun-nosuke Teramae and everyone joined the seminar. Reported by Yingying Xu
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2022-07-15
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Quantum Matter Seminar by Dr. Ken Shiozaki on July 12, 2022
Prof. Ken Shiozaki gave a seminar about adiabatic cycles of quantum spin systems. Topological phases of matter without ground state degeneracy are known as inevitable phases. In the literature, their topological properties have been well-studied in free-fermion and many-body systems. The speaker started with the transverse-field Ising model and the Rice-Mele model to demonstrate the pumping of the 1D chain in an adiabatic cycle. He then generalized the concept to cover broader systems, including general spatial dimensions and generic models with any onsite symmetry, such as time-reversal, Z2 Ising, and U(1). He demonstrated that one can classify adiabatic cycles of a spin model, which can be characterized by a Z2 topological invariant. This talk showed that symmetry-protected topological phases emerge by performing an adiabatic cycle. Reported by Chen-Hsuan Hsu (YITP, Kyoto University)
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2022-07-13
セミナーレポートiTHEMS Theoretical Physics Seminar by Prof. Hiroshi Suzuki on July 5, 2022
The iTHEMS-phys intensive lecture was held on July 5 and 6, 2022. The speaker is Prof. Hiroshi Suzuki at Kyushu University. The title is “Gradient flow exact renormalization group.” 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. Recently, he has proposed a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. He has explained the basic idea and properties of GFERG. He has also presented a possible application of GFERG to the consideration of the axial anomaly. The lecture was held via Zoom. There were about 30 participants from iTHEMS and other universities. The participants enjoyed fruitful discussions throughout the lecture. Reported by Kengo Kikuchi
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2022-07-06
セミナーレポート
iTHEMS Biology Seminar by Mr. Keiichi Morita on June 23, 2022
I talk about how evolution of sexual traits such as ornaments of guppies can affect coexistence of two closely related species. First, I introduce "reproductive interference," sexual interaction driving evolution of sexual traits. Second, I show how to formulate population dynamics of two closely related species with reproductive interference. Next, I introduce mathematical modeling of quantitative genetics in order to formulate trait evolution. Finally, I show results of analysis and simulation by combining population dynamics and evolution (i.e., eco-evolutionary feedbacks). In future works, I should the effect of costs of evolution or the other species. Thank you for your listening and giving me comments! Reported by Keiichi Morita
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2022-07-05
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Quantum Matter Seminar by Dr. Thore Posske on June 30, 2022
Dr. Thore Posske from the University of Hamburg gave an online seminar about controlling topological quantum effect in spin systems by manipulating the boundary. He first introduced the idea that topology can connect multiple subfields in physics and then showed how a 1D spin chain can be controlled to form a helix or the ground state by manipulating the evolution of the two chain ends. Since the different quantum states can be controlled by the boundary, this is a potential platform for quantum computing to generate distinct quantum states. Furthermore, the boundary idea was extended to 2D spin systems. By properly changing the spins on the edges, a skyrmion can emerge. In the end, the speaker talked about an experimental approach to distinguishing the topological phases in systems with periodic boundary conditions by multi-pulse spectroscopy, and applied these ideas to 1D topological superconductors. Reported by Thore Posske (University of Hamburg) and Ching-Kai Chiu
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2022-07-04
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ABBL-iTHEMS Joint Astro Seminar by Mr. Tomoki Matsuoka on July 1, 2022
Mr. Tomoki Matsuoka gave an excellent talk on the long-term evolution of a supernova remnant hosting a double neutron star binary. He presented that stellar mass loss is one of the crucial elements determining the fate of core-collapse supernovae progenitors (SNe). Since the material released from the progenitor will be distributed as circumstellar medium (CSM), it can also influence 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, he investigated the dynamical evolution of an ultra-stripped supernova remnant (USSNR), which originated from a core-collapse SN explosion proposed to be a candidate formation site of a double neutron star binary. By accounting for the mass-loss history of the progenitor binary using a model developed by a previous study, he constructed the large-scale structure of the CSM up to a radius ∼100 pc. Then, he simulated the explosion and subsequent evolution of a USSN surrounded by such a CSM environment. He found that the CSM encompasses a vast 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, he talked about the background of the connection between the models for stellar evolution and SNRs, the details of his methods, and future prospects very well. Reported by Shigehiro Nagataki
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2022-07-04
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iTHEMS Biology Seminar by Dr. Margie Mayfield on June 30, 2022
Dr. Margie Mayfield (University of Melbourne) gave us a fantastic talk in the special biology seminar, held in a hybrid style at Okouchi Hall. She told us about comparative work on theoretical models and data in wild flowers. We really thank Margie on her great talk, especially despite her very tight schedule in Japan. Thank you Margie! I look forward to seeing you soon in person! Reported by Ryosuke Iritani
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2022-06-27
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iTHEMS Math Seminar by Dr. Shou Yoshikawa on June 10, 2022
On June 10, Shou Yoshikawa gave an introductory talk on his research field. He started his talk by explaining what is an algebraic geometry in mixed characteristic. He then explained some recent results on this subject. Reported by Keita Mikami
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2022-06-23
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Quantum Matter Seminar by Dr. Nobuyuki Okuma on June 21, 2022
Quantum Matter Study Group invited Prof. Nobuyuki Okuma to give an online seminar about non-Hermitian topological phases. The seminar started with a succinct introduction to non-Hermitian matrices. Different from Hermitian systems, the energy spectra now become complex numbers, the bra and ket states become inequivalent, and the Hamiltonians are not always diagonalizable, leading to the emergence of exceptional points. Taking the Hatano-Nelson model as an example, the speaker studied the 1D chain with the imaginary gauge transformation and showed that the spectra strongly depend on the boundary conditions (being periodic or open). Furthermore, distinct from end modes in Hermitian topological insulators, skin effect arises in non-Hermitian systems, with skin modes accumulating in one end of the chain. He further showed that this skin effect also exhibits topological nature and can be generalized to either higher-dimensional systems or to other non-Hermitian systems with Z2 topological invariants. Reported by Chen-Hsuan Hsu (YITP) and Ching-Kai Chiu
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2022-06-21
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iTHEMS Biology Seminar by Dr. Mitsusuke Tarama on June 16, 2022
On June 16th, Dr. Tarama gave us an interesting talk about the physical modeling of self-organization in the chick embryo. He first introduced several beautiful patterns in biology such as stripes of pigment cells of Zebrafish. He then explained a recent observation of the dynamical meshwork structure of chick mesodermal cells, which is the direct motivation of his theoretical work. He showed how the intercellular interactions and shape deformation of cells can produce the dynamical meshwork structure, by physical modeling and application of the persistent homology as a useful tool. We are really grateful to Dr. Tarama for his comprehensive talk from both experimental and theoretical sides. Reported by Kyosuke Adachi
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2022-06-20
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Math-Phys Seminar by Dr. Daisuke Yoshida on June 16, 2022
Dr. Daisuke Yoshida first motivated the expectation that the true quantum gravity, whatever its form turns out to be, should be free from singularities in the universe. The "singularity theorem" by Penrose states that a spacetime singularity arises under a set of certain assumptions. Flipping the argument around, if one admits that singularities are absent in our universe, at least one of the assumptions in the theorem needs to be abandoned. Dr. Yoshida discussed general properties that a non-singular universe must satisfy in order to avoid the singularity theorem. In particular, he found and explained that the universe must be, in some sense, smaller than the corresponding closed de Sitter spacetime. His talk stimulated the audience, and they continued discussions for long after his seminar. Reported by Ryo Namba
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2022-06-09
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iTHEMS Biology Seminar by Dr. José Said Gutiérrez-Ortega on June 2, 2022
In this talk, I mentioned how both geographic isolation and natural selection may influence the way how species can be originated. I made emphasis in a general pattern that suggests that tropical species are more likely than high-latitude species to evolve while retaining the niche of their ancestors; a process called “niche conservatism”. To demonstrate this pattern, I showed the recent results of my own empirical research on the cycad genus Ceratozamia from Mexico: species at lower latitudes evolved niches less differentiated than expected from a Brownian Motion model (an evidence of niche conservatism), and high-latitude species evolved niches more differentiated than expected (an evidence of niche divergence). I hypothesize that both “niche conservatism” and “niche divergence” are not opposed processes as usually thought in ecology, but are part of a same general process. The implementation of models to predict how phylogenetic and ecological factors interplay in the formation of species along the latitudinal gradient may explain the pattern at the global level. The discussion on this topic allowed identifying that the latitude-associated variation of biodiversity richness seems to be analogous to thermodynamic models: a higher energy availability in the tropics will make biological groups to evolve different ways (species) to exploit that energy. Reported by José Said Gutiérrez-Ortega
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2022-06-08
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DMWG Seminar by Dr. Shintaro Eijima on June 6, 2022
Dark matter (DM) is one important ingredient of our Universe of which existence indicates the theory beyond the Standard Model. It is not the unique motivation to extend the Standard Model describing the visible world. For example, we need to explain the origin of the tiny neutrino mass and the matter-antimatter asymmetry. The introduction of sterile neutrinos could solve these problems simultaneously. Sterile neutrinos are new species of neutrinos which communicate with the Standard Model neutrino (active neutrinos) through mixing. Unfortunately, the possibility of explaining the whole of DM with the sterile neutrinos is already excluded from observations of X-ray emission, neutrino beam experiments, and cosmological requirements. However, it is still a viable candidate when we consider the production mechanism carefully. Furthermore, some of such scenarios expect large lepton asymmetries resulting in the matter-antimatter asymmetry. The sphaleron process takes an important role in such scenarios and it is related to the electroweak phase transition in the early Universe. The process of fixing the lepton asymmetry is interesting: sterile neutrinos first freeze-in, then freeze-out, and decay. Quantitative prediction of such processes requires sophisticated calculations. Dr. Eijima has shown the latest results in this talk, with the comments that the bottleneck to proceed is the computational costs. The methodology is already well-developed. We will see indicative predictions in the near future! Neutrino physics will open new windows for our Universe! Reported by Nagisa Hiroshima
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2022-06-08
セミナーレポート
ABBL-iTHEMS Joint Astro Seminar by Dr. Kanji Mori on June 3, 2022
Axion-like particles (ALPs) are a class of hypothetical bosons that feebly interact with ordinary matter. The hot plasma of stars and core-collapse supernovae is a possible laboratory to explore physics beyond the standard model, including ALPs. Once produced in a supernova, some of the ALPs can be absorbed by the supernova matter and affect energy transfer. The speaker recently consistently calculated the ALP emission in core-collapse supernovae and the backreaction on supernova dynamics. It is found that the stalled bounce shock can be revived if the coupling between ALPs and photons is as high as $g_{a\gamma}\sim 10^{-9}$ GeV$^{-1}$ and the ALP mass is 40-400 MeV. Reported by Shigehiro Nagataki
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2022-05-30
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Math-Phys Seminar by Dr. Toshifumi Noumi on May 19, 2022
Dr. Toshifumi Noumi (Kobe University) gave a pedagogical seminar on the so-called swampland program in particle physics. The program aims to clarify nontrivial consistency conditions on symmetries in quantum gravity that leave implications for particle physics and cosmology. Dr. Noumi started out with the basic philosophy of the study and expanded the details using the arguments of symmetries, blackholes, holography etc., keeping accessibility for broad audience. Reported by Ryo Namba
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2022-05-30
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iTHEMS Math Seminar by Dr. Yuto Moriwaki on May 23, 2022
On May 23, there was a math seminar by Yuto Moriwaki. He gave an introductory talk on the mathematical formulation of CFT. Reported by Keita Mikami
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2022-05-30
セミナーレポート
iTHEMS Biology Seminar by Dr. Dan Warren on May 19, 2022
In the Biology Seminar on May 19th, 2022, we had the great opportunity to have Dr. Dan Warren (Okinawa Institute of Science and Technology, Japan) as an invited speaker. In his talk, Dr. Warren explained why the evaluation of species distribution models (SDMs) has become a useful method to understand and predict the geographic distribution of species. In particular, they provide vital information to take measurements in the conservation of biodiversity. To construct SDMs, researchers in this field have taken advantage of publicity available geographic and environmental big data. Usually, those kind of data were not produced with the intention to use it in ecology, but ecologists have developed many methods to use the big data to answer questions in ecology and evolutionary biology. However, despite that several of those methods have become standard in ecology, Dr. Warren warns us that all commonly used methods have serious biases, and such biases might be related to how much we unquestionably rely that big data. To explain his point, he showed the results of one paper that he and his colleagues recently published. In that paper, the authors used occurrence data of a fictional animal: the Pokémon Kangaskhan (name in English) or ガルーラ (in Japanese), and followed the usual methods to construct SDMs in order to predict the Pokémon distribution in the Australian territory. They found that the distribution of the fictional animal has strong biases, and that same patterns of biases are also present in many other real-life species. Dr. Warren concluded that there is a big open field to improve methods to construct SDMs. The incorporation of prior information in the construction of SDMs, and the application of Markov chain Monte Carlo methods to account for the uncertainty of results might be effective solutions to solve the problems that persist in this research field. Reported by José Said Gutiérrez-Ortega
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2022-05-30
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Seminar by Dr. Teppei Kitahara on May 20, 2022
Dr. Teppei Kitahara from Nagoya University gave a comprehensive review of anomalies from the Standard Model in particle physics. Continuous development of experiments in recent years has revealed a large number of experimental anomalies which the Standard Model cannot explain. It is statistically obvious that as the number of experiments increases, one encounters a new anomaly due to the statistical fluctuation. But interestingly, some of the anomalies have been cross-checked by different experiments. These would be hints for physics beyond the Standard model. In his seminar, he focused on the flavor anomalies (also known as lepton flavor universality violation), the muon g-2 anomaly, and recently measured the W boson mass anomaly. He also discussed these implications for the new physics and introduced several of his works. Reported by Etsuko Itou
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2022-05-23
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ABBL-iTHEMS Joint Astro Seminar by Dr. Yannis Liodakis on May 20, 2022
The origin of high-energy neutrinos is fundamental to our understanding of the Universe. Apart from the technical challenges of operating detectors deep below ice, oceans, and lakes, the phenomenological challenges are even greater. The sources are unknown, unpredictable, and we lack clear signatures. Neutrino astronomy therefore represents the greatest challenge faced by the astronomy and physics communities thus far. The possible neutrino sources range from accretion disks and tidal disruption events, through relativistic jets to galaxy clusters with blazar TXS 0506+056 the most compelling association thus far. Since then, immense effort has been put into associating AGN-jets with high-energy neutrinos, but to no avail. The speaker discussed his current efforts in understanding the multimessenger processes in the Universe, and once and for all proving or disproving if AGN-jets are neutrino emitters. Reported by Shigehiro Nagataki
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2022-05-18
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iTHEMS Math Seminar by Dr. Taketo Sano on May 13, 2022
In May 13, there was a math seminar by Taketo Sano. He gave an introductory talk on category theory. Reported by Keita Mikami
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2022-04-30
セミナーレポート
iTHEMS Biology Seminar by Mr. Daiki Kumakura on April 28, 2022
On April 28th, I talked about the Asgard archaea and the theory of intracellular symbiosis and discussed the mathematical modeling of the symbiosis hypothesis. First, I gave a brief of the classification of the organism as a five-kingdom system and three-domain system. Next, I talked about Asgard archaea, a group of archaea that has received much attention recently. Finally, I discussed the culture of Asgard archaea and the new theory of intracellular symbiosis that has developed as a result. In my presentation, I prepared the idea of mathematical modeling for the new theory. Audience members gave a variety of opinions on this model. In particular, I discussed points where the evolutionary model should be added, whether deterministic or stochastic dominance contributed, and why symbiosis was possible only in two specific species although a variety of symbiotic relationships were possible. I had a meaningful time exchanging opinions and having discussions with various researchers. Thank you so much. Reported by Daiki Kumakura
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2022-04-28
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iTHEMS Colloquium by Dr. Hong-Yan Shih on April 22, 2022
On April 22 (Fri), we had the first iTHEMS colloquium of FY2022 by inviting Hong-Yan Shih from Academia Sinica, Taiwan. After reviewing the turbulent phenomena in various area of science, she discussed how the turbulence occurs by increasing the flow velocity and how one can develop an effective theory to describe the critical region of laminar-turbulent transition. Then she discussed a remarkable mathematical relation between the effective theory with the predator-prey dynamics in ecology and showed a characteristic super exponential scaling law. The topic was an ideal subject for the interdisciplinary talk, and there were many questions from the researchers with different scientific backgrounds.
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2022-04-28
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Introduction to Topological Insulators by Dr. Tomoki Ozawa on April, 2022
In this lecture series, Professor Ozawa gave an introduction to topological insulators which are materials whose wavefunctions show nontrivial topological structures in momentum space. In the first two lectures, he introduced the so-called Su-Schrieffer-Heeger model and the bulk-edge correspondence which links edge states with winding number of certain operator in the Hamitonian. Such correspondence has its origin in mathematics called Toeplitz Index theorem which is a special case of Atiyah-Singer index theorem. In the last two lectures, Chern insulators and quantum metrics are introduced. Eigenvectors of the Hamiltonian define a map from the momentum space (typically a torus) to a complex projective space. The pullback Fubini-Study metric (and standard Kahler form) defines the so-called quantum metric (and Berry curvature) on the momentum space. Using Chern-Weil theory, Chern classes/characters are then defined. Chern classes which are originally notions from differential geometry/topology play an important role in topological insulators. A necessary and sufficient condition is also given when the above mentioned map is an immersion and realises momentum space as a Kahler submanifold of the projective space. Reported by Yalong Cao
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2022-04-25
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iTHEMS Math Seminar by Dr. Cédric Ho Thanh on April 22, 2022
On April 22, there was a math seminar by Dr. Cédric Ho Thanh. In the first half, he explained the recurrence theorems for the topological Markov chain. In the second half, he explained the sketch of the proof. Reported by Keita Mikami
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2022-04-25
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ABBL-iTHEMS Joint Astro Seminar by Dr. Masanori Iwamoto on April 22, 2022
Dr. Masahiro Iwamoto gave a presentation on his recent three-dimensional (3D) particle-in-cell (PIC) simulation of relativistic shocks and application of the results of the 3D-PIC simulations to astrophysical phenomena. For example, the origin of fast radio bursts (FRBs; Lorimer et al. 2007) is one of the unsolved problems in astrophysics. Many observations of FRBs indicate that FRBs must be coherent emission in the sense that coherently moving electrons radiate electromagnetic waves. In relativistic shocks, it is well known that coherent electromagnetic waves are excited by synchrotron maser instability (SMI) in the shock transition (Hoshino & Arons 1991). The SMI is also known as the emission mechanism of coherent radio sources such as auroral kilometric radiation at Earth and Jovian decametric radiation. Recently, some models of fast radio burst based on the coherent emission from relativistic shock via the SMI have been proposed (e.g., Lyubarsky 2014; Beloborodov 2017; Plotnikov & Sironi 2019; Metzger et al. 2019) and the SMI in the context of relativistic shocks attracts more attention from astrophysics. In this seminar, by performing the world’s first 3D-PIC simulation of relativistic shocks, he demonstrated that large-amplitude electromagnetic waves are indeed excited by the SMI even in 3D and that the wave amplitude is significantly amplified and comparable to that in pair plasmas due to a positive feedback process associated with ion-electron coupling. Based on the simulation results, he discussed the applicability of the SMI for FRBs. Reported by Shigehiro Nagataki
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2022-04-14
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iTHEMS Biology Seminar by Dr. Hiroshi Yokota on April 14, 2022
In iTHEMS biology seminar on April 14th, I introductory talked about the coarse-grained molecular dynamics simulation by using Langevin equation which is the equation of motion including the interaction, the friction and the random force. First, I mentioned the chromosome formation dynamics as an example of the application range of the simulation. Next, I explained the Langevin equation and its intuitive picture. Then, I showed the discretized Langevin equation which keeps the stochastic properties of the random force term. Finally, I showed some examples of Langevin simulation. Many questions and discussions arose from the audience. Thank you very much!
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2022-04-01
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iTHEMS Biology Seminar by Dr. Euki Yazaki on March 17, 2022
At the March 17th seminar , I presented my research. It was mainly an analysis of the phylogenetic position of orphan organisms (organisms whose phylogenetic position is unknown) based on large-scale sequence data, and in addition, I showed that huge lineages (Archaeplastida), including plants, are monophyletic. Although monophyly of Archaeplastida has been debated for many years, this study clarified that they are monophyletic and why they were not monophyletic in previous research. The seminar was very active, with many questions about the methods of phylogenetic analysis and biological questions.
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2022-03-30
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Quantum Matter Seminar by Dr. Tiantian Zhang on March 24, 2022
The Quantum Matter Study Group invited Dr. Tiantian Zhang from Tokyo Institute of Technology to talk about the local and global topology for Tg-protected Z2 Dirac points. In the beginning, by introducing the topological phase in the gapped and gapless systems, she discussed the conventional and Z2 Dirac points. Surprisingly, she established gauge-invariant charge formula and bulk-surface correspondence for Z2 Dirac points, which can give a full understanding about the topology of Tg-protected Z2 Dirac points. Then, she proposed the first Z2 Dirac material candidate Li2B4O7 for further exploration. Reported by Congcong Le
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2022-03-25
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How is mathematics utilized in society? - Exploring the Essence of Mathematical Research Special Lecture by Shigefumi Mori and Takashi Sakajo on March 12, 2022
On March 12, a zoom discussion by two mathematicians, Takashi Sakajyo (Kyoto U./iTHEMS) and Shigefumi Mori (KUIAS/iTHEMS), was held as an iTHEMS x academist special event "How is mathematics utilized in society?" More than 380 people from academia, schools, and companies have joined online. After the introductory talks on the usefulness of mathematics in modern times by Sakajyo san, and on the beauty and joy of mathematics by Mori san, they had interesting discussions on three topics, the relation between mathematics and society, mathematics education, and how do mathematicians face mathematical problems? Reported by Tetsuo Hatsuda
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2022-03-22
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iTHEMS Math Seminar by Dr. Lin Li on March 18, 2022
In March 18, there was a seminar by Dr. Lin Li. He explained his theoretical research on the control of hurricane. The main difficulty is that the order of the energy of the so large that it is 106 times larger than the energy we could use. To overcome this difficulty, he explained some ideas and his simulation on how his ideas will work. Reported by Keita Mikami
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2022-03-15
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iTHEMS Math Seminar by Dr. Pengyu Liu on March 11, 2022
In March 11, there was a math seminar by Dr. Pengyu Liu from computational climate science research team. In the first part, he explained two extract rules to obtain Boolean function from the neural network. In the second part, he explained how we can apply results in the first part to predict human Dicer cleavage sites. Reported by Keita Mikami
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2022-03-15
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iTHEMS Math Seminar by Dr. Shigenori Nakatsuka on January 28, 2022
Dr. Shigenori Nakatsuka from Kavli IPMU gave us a talk on dualities in W-superalgebras. In the first half of the talk he reviewed some basic concepts of vertex superalgebras, in particular W-superalgebras, and the Feigin--Frenkel duality, which states that the W-algebras in a certain class are isomorphic to the other W-algebras associated with the dual Lie algebras and the dual levels. In the latter half of the talk he introduced dualities beyond the Feigin--Frenkel duality including his recent work with Creutzig, Genra, and Sato. One of the remarkable results is the proof of the Feigin--Semikhatov conjecture, which gives a correspondence between the W-algebras associated with certain Lie algebras and the W-superalgebras associated with the corresponding Lie superalgebras. His talk was so stimulating that we could enjoy the mathematics of W-algebras. Reported by Mizuki Oikawa
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2022-03-11
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iTHEMS - R-CCS(FTRT) Joint Online Seminar by Prof. Gergely Fejos on February 18, 2022
On Feb.18, 2022, Dr. Gergely Fejos (Eotvos Lorand Univ., Hungary) gave a talk at the first iTHEMS - R-CCS(FTRT) Joint Seminar. He reported a functional renormalization group study of the three dimensional Ginzburg--Landau potential for the chiral phase transition in three flavor quantum chromodynamics. The order of the phase transition in this system has long been thought to be first-order, but his conclusions suggest the possibility of a second-order phase transition. A lively discussion took place between the speakers and the audience on this interesting result. Reported by Tetsuo Hatsuda
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2022-03-10
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ファンダメンタルズ フェスmini プレイベント 科学篇 「探究と架橋：基礎科学の可能性」が2022年3月10日に行われました
2022年3月10日に基礎科学と社会の関わりをテーマにして討論会が開催されました。数学者の佐々田さん、人類学者の山極さん、そして物理学者の初田さんが、アーテイストの坪井あやさんをモデレータに、自然科学と社会科学における普遍性とは何か、基礎科学と社会を繋ぐ”触媒”としての科学者の役割などについて、活発な議論が行われました。 動画はyoutubeで配信されていますので、ぜひ関連リンクを御覧ください。
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2022-03-10
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iTHEMS Biology Seminar by Prof. Atsushi Mochizuki on March 10, 2022
In this week’s biology seminar, with great honor, we have Prof. Mochizuki to give us an interesting talk on “Independent regulation of multiple checkpoints in cell-cycle network system-Biological function originated in the law of localization-”. He showed us how mathematical analysis about the complex cell cycle networks can provide knowledge on non-trivial behaviors in regularization systems. The transformation from complex cell cycle networks to structural sensitivity matrix is amazing. He and his collaborator found the “buffering structure” which are essential local characters as the origin of biological function. Furthermore, “buffering structure” can generally appear in chemical reaction network including complex formation. He specially studied the G1-S and G2-M checkpoints in cell cycle. The analyses clarified that, even the two checkpoints are regulated by different protein complexes (Cdc2-Cdc13 and Cdc2-Cig2, respectively) with common species of proteins and activation reactions conform a complicated network, these two complexes are regulated by disjoint sets of reaction parameters in the system. We are looking forward to the further study of comparison with cell cycle experimental data. Many questions and discussions arose from the audiences. We appreciated very much the time Prof.Mochizuki shared with us. Reported by Yingying Xu
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2022-03-09
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iTHEMS Biology Seminar by Dr. Shingo Gibo on February 17, 2022
Many biological time-series data are not stationary, which makes it difficult to analyze the instantaneous phase and amplitude. In the iTHEMS Biology seminar on February 17, I talked about Hilbert transform, which is known as a method to estimate the phase and the amplitude dynamics of nonstationary time-series. First, I explained the mathematical background of the method. Then, I introduced some applications of this method to chronobiology, virus dynamics, and acoustic engineering. In this seminar, there were many questions and comments from audiences. Thank you very much!
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2022-03-09
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ABBL/iTHEMS Astro Seminar by Dr. Yuta Sekino on February 18, 2022
On 18th Feb. 2022, Dr. Yuta Sekino gave an excellent introductory talk on Spin transport in ultracold atomic gases. In his talk, we discussed the usefulness of spin transport as a probe for many-body properties in ultracold atoms. In the first part, we focused on the conductivity of alternating spin current, which includes information on superfluid gap, pseudogap, and topological phase transition. In the latter part, we considered mesoscopic spin transport between two Fermi gases weakly connected with each other. Finally, we discussed similarities of ultracold atoms to neutron star matter. Reported by Shigehiro Nagataki
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2022-03-01
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iTHEMS Biology Seminar by Dr. Ashley Nord and Dr. Rubén Pérez-Carrasco on February 24, 2022
Dr. Ashley Nord (Centre de Biologie Structurale/CNRS, France) and Dr. Rubén Pérez-Carrasco (Imperial College London, UK) gave a very interesting talk on the dynamics of stator units, the ion channels that generate torque for bacterial flagella. In the first half of the presentation, Dr. Ashley explained how the stator units produce torque once they are bound to the flagellar structure. Their experiment was able a) to track magnetic nanoparticles attached to E. coli flagella, and b) to set two initial conditions for the number of bound stator units. The work differs from the traditional views of the field because it shows -- for the first time -- the existence of two sets of relaxation times for stator units [1,2]. In the second part of the talk, Dr. Rúben discussed various stochastic models with asymmetric relaxation times to describe the dynamics of stator units. According to estimates via approximate Bayesian computation, the extended catch bond model with additional bound states performed better than other alternatives. If confirmed, their conclusion could give important hints and improve our understanding of biochemical processes in flagellar motors. Reported by Gilberto Nakamura
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2022-02-28
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Quantum Matter SG seminar by Dr. Hong-Yan Shih on February 24, 2022
The Quantum Matter Study Group invited Dr. Hong-Yan Shih from Academia Sinica to talk about the phase transitions of turbulence dynamics. In the beginning, she introduced the turbulence and the phase transition between laminar flow and turbulence. Surprisingly, this phase transition shares a unified picture with the predator-prey system. Then, she showed the connection between this fluid dynamics and the biosystem with the same university class. It is an inspiring interdisciplinary study. Reported by Ching-Kai Chiu
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2022-02-21
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iTHEMS Math Seminar by Dr. Genki Hosono on January 14, 2022
Dr. Genki Hosono gave us a stimulating talk on pluripotential and $L^2$ methods in complex geometry. The talk was carefully designed not only for non-mathematicians but also for experts around the topic. He began his talk with the definition and basic properties of subharmonic function and its multivariable version in complex geometry: plurisubharmonic function. He then introduced Bergman kernel and explained a variational approach to Ohsawa-Takegoshi $L^2$ extension theorem, which is an extension theorem of holomorphic function with a bound on $L^2$ norm weighted by a plurisubharmonic function. Finally he explained Deng-Wang-Zhang-Zhou’s result on a `reverse direction’ of Ohsawa-Takegoshi theorem and his result with Inayama on a variant result. His explanations were very clear and quite valuable for us. Reported by Eiji Inoue
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2022-02-21
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NEW WG Seminar by Mr. Takumi Hayashi on February 15, 2022
Takumi Hayashi (Tokyo/RESCEU) gave a talk on Lorenzian path-integral approach to false vacuum decay [1]. Conventionally, false vacuum decay has been discussed within the Euclidean formalism developed by Coleman, but it may suffer from several subtle issues when applying to cosmological problems. Takumi proposed a new formulation for false vacuum decay and computed the bubble nucleation rate by directly evaluating a Lorenzian path integral based on the Picard-Lefschetz theory. Takumi discussed nucleation of bubbles with various sizes, not limited to the critical one only to which the Euclidean formalism can be applied, and showed that nucleation of small bubbles is more probable than the critical one. More than 20 physicists have joined the seminar and enjoyed fruitful discussions. Reported by Hidetoshi Taya
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2022-02-16
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ABBL/iTHEMS Astro Seminar by Dr. Yutaka Hirai on January 28, 2022
Dr. Yutaka Hirai gave an excellent talk on Galactic archaeology with r-process elements. He showed that his high-resolution simulations of galaxies suggest that binary neutron star mergers play an important role in enriching r-process elements in dwarf galaxies and the Milky Way. He also showed that r-process enhanced stars in the Milky Way tend to form in dwarf galaxies previously accreted to the Milky Way. He demonstrated that the abundance of r-process elements in stars can be used as an indicator for the early evolution of the Milky Way. Reported by Shigehiro Nagataki
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