News
187 news in 2020
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2020-04-09
Person of the Week
Self-introduction: Euki Yazaki
My name is Euki Yazaki and I joined iTHEMS in April 2020. My research area is biology, and I have been studying evolutionary biology consistently since I started my research career as a student at University of Tsukuba in 2010. I am particularly interested in the molecular phylogeny and molecular evolution of eukaryotic microorganisms (called Protists). Based on large-scale molecular sequence data acquired from many Protists, I have inferred the evolutionary history of genes and phylogenetic relationships of organisms. Ultimately, I hope to elucidate the early evolution of eukaryotes. I'm very excited to be a member of iTHEMS because the mathematical professionals from diverse backgrounds at iTHEMS give me the opportunity to expand my biology and therefore my science.
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2020-04-07
Announcement
Dr. Tomoki Ozawa's article, "Study of Topological Lattice Models with Synthetic Dimensions" was published
The article written by Dr. Tomoki Ozawa, "Study of Topological Lattice Models with Synthetic Dimensions" was published in the April 2020 issue of Butsuri, the monthly magazine published by Physical Society of Japan. The cover of the same issue was based on a figure from the article by Dr. Ozawa. For more details, please refer to the article by him in this issue.
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2020-04-06
Hot Topic
Current status of training and co-creation -- Researcher thinking and technology required for innovative human resources
The CNET Japan Live 2020 held on February 19, various performances talk about the theme of "Innovation indispensable for corporate growth". Mr. Hiroyasu Kodama at G's ACADEMY and Dr. Tsukasa Tada at Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) in RIKEN are trying to create and nurture innovators and work on co-creation with companies. A panel discussion entitled “Developing and co-creating innovators” was held.
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2020-04-06
Person of the Week
Self-introduction: Akira Dohi
Hello, I am Akira Dohi, the Junior Research Associate (JRA) student. My research interest concentrates on how neutron stars are cooled or heated. A Neutron star is born as a remnant by supernova explosion of a massive star and basically cools down by many neutrino losses. How to cool or heat the neutron star is connected to the temperature or magnetic field of the surface, which can be estimated using the observations of X-ray astronomical satellite. The cooling and heating processes are believed to be caused in a wide range of density regions even with the above nuclear saturation density. I am studying numerical modeling of neutron stars evolution, and combining some observations, I aim to specify the origin of these processes, which would be useful for elucidation of various physics, above all nuclear theory. iTHEMS’s members have different fields from my area and this would broaden our scientific knowledges and views through communications.
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2020-04-06
Person of the Week
Self-introduction: Masaki Taniguchi
I am Masaki Taniguchi, a mathematician, who has been working at iTHEMS/RIKEN since April 2020. My interests cover gauge theory, Floer theory and its applications to 3- and 4-dimensional topology. In a mathematical study of gauge theory, we obtain information of 4-manifolds by observing the moduli space of solutions to a certain non-linear partial differential equation for a given 4-manifold. This method enables us to find interesting phenomena of 3- and 4-dimensional topology which are different from that of other dimensions. Currently, I am studying the following topics: 1. gauge theory for a class of non-compact 4-manifolds called 4-manifolds with periodic ends and their applications to existence of codimension-1 embedding of 3-manifolds and positive scalar curvature on spin 4-manifolds, 2. a quantitative formulation of instanton Floer homology and its applications to a study of the homology cobordism group which is related to existence of triangulations of topological manifolds, and 3. a study of 2-dimensional knots in the 4-space using gauge theory. I'm also interested in physical aspects of gauge theory. I'm looking forward to discussing with researchers in various fields at RIKEN.
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2020-04-06
Person of the Week
Self-introduction: Ryusuke Hamazaki
My name is Ryusuke Hamazaki. I am a senior research scientist at iTHEMS and also a RIKEN Hakubi leader of a team on nonequilibrium statistical mechanics. So far I have worked on foundation of equilibrium quantum statistical mechanics, namely how isolated quantum many-body systems relax to thermal equilibrium after long time. Extending this framework, I am currently trying to understand laws of nonequilibrium quantum statistical mechanics. Another motivation of mine is to apply the theory to other nonequilibrium science, such as biology or high-energy physics. I am eager to discuss and collaborate with one another to contribute to interdisciplinary fields through universality of statistical mechanics!
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2020-04-03
Hot TopicCoffee Meeting with zoom streaming on April 3, 2020
At the weekly coffee meeting on April.3 (Fri.), Haoning He (ABBL) gave a nice explanation of "Multi-meesenger Search for sources of high energy neutrino". Almost 40 member of iTHEMS accessed on the virtual meeting.
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2020-04-03
Seminar Report
Math Seminar Talk by Dr. Mikio Furuta, February 25, 2020.
Prof. Mikio Furuta from the University of Tokyo gave a talk at the Math Seminar on February 25, 2020. The title of his talk was "Index of the Wilson-Dirac operator revisited: a discrete version of Dirac operator on a finite lattice". His talk was based on his recent collaboration with both mathematicians and physicists. The main goal of his talk is to give an equality between the index of the Dirac operator, which is defined on a continuous space, and that of the Wilson-Dirac operator, which is defied on a discrete lattice. This equality is given in a suitable K-group, which is defined as a collection of (some equivalence classes of) pairs of Hilbert spaces and operators acting on them. The key point in the proof of the main result is to compare two different Hilbert spaces somehow, and he explained an idea of the construction of a map needed for this comparison. This talk included many new ideas, and both of mathematicians and physicists enjoyed it very much.
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2020-04-01
Hot Topic
Coffee Meeting with zoom streaming on March 27, 2020
On March 27 (the last Friday in FY2019), the first zoom coffee meeting in iTHEMS was held. Many iTHEMS colleagues have connected virtually to the iTHEMS common room. Takemasa Miyoshi gave a 15 min. talk on SIR model of epidemics followed by 1 min. farewell speeches by the people who graduated iTHEMS and/or QHP lab. at the end of FY2019. From FY2020, all the iTHEMS coffee meetings and colloquiums will be held only through zoom for a while to suppress the physical interactions among researchers and at the same time to increase their virtual interactions.
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2020-03-31
Hot Topic
Farewell messages to the colleagues leaving iTHEMS from Tetsuo Hatsuda
I would like to congratulate iTHEMS colleagues who are moving to other places from April 1, 2020. Masato Taki (-> Rikkyo Univ.) Yosuke Kubota (-> Shinshu Univ.) Susumu Inoue (-> RIKEN ABBL) Hokuto Konno (-> Univ. Tokyo) Yoshimasa Hidaka (-> KEK) Koya Sakakibara (-> Okayama U. of Science) Shinya Gongyo (-> DENSO IT Lab.). Also I would like to thank Atsushi Mochizuki (Kyoto Univ.), who is one of the founding members of iTHEMS, for his long standing contributions. He will step down as an iTHEMS Deputy Director and will serve for iTHEMS Senior Research Scientist from FY2020. Last but not the least, I would like to thank Motoko Kotani (RIKEN Executive Director) who has served for iTHEMS Scientific Advisor and will move to Tohoku Univ. from April 1, 2020. I wish you all have great success in new places! with best regards, Tetsuo
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2020-03-30
Award
Dr. Yosuke Kubota receives 11th annual RIKEN Research Incentive Award
Yosuke Kubota received "RIKEN Excellent Achievement Award (理研梅峰賞)" on March 12, 2020 for his achievements in the "Equivariant KK-theory and the Atiyah-Segal completion". Congratulations!
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2020-03-30
Award
Dr. Hirotaka Ito receives 11th annual RIKEN Research Incentive Award
Hirotaka Ito received "RIKEN Excellent Achievement Award (理研梅峰賞)" on March 12, 2020 for his achievements in the "Theoretical study on the origin of the correlation between spectrum and brightness of gamma-ray bursts". Congratulations!
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2020-03-24
Award
Dr. Ryosuke Iritani received Suzuki Prize of The Ecological Society of Japan
Ryosuke Iritani received "Suzuki Prize of The Ecological Society of Japan" on March 7, 2020, for his contribution to a wide range of evolutionary ecology as an early career theoretical researcher. Congratulations, Ryosuke!
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2020-03-19
Research News
RIKEN Research: Merger between two stars led to iconic supernova -- Simulations suggest that two stars came together to form a blue supergiant, which subsequently exploded
A supernova in a nearby galaxy may have originated from an explosion of a blue supergiant formed by the merger of two stars, simulations by RIKEN astrophysicists suggest1. The asymmetric nature of this explosion may provide hints for where to look for the elusive neutron star birthed in this stellar cataclysm. A core-collapse supernova occurs when the core of a massive star can no longer withstand its own gravity. The core collapses in on itself, triggering a violent explosion that blasts away the star’s outer layers, leaving behind a neutron star or black hole. In 1987, astronomers saw a star explode in the Large Magellanic Cloud, one of our galaxy’s closest neighbors. Since then, scientists have intensively studied the aftermath of this supernova, known as SN 1987A, to understand the nature of the progenitor star and its fate. The progenitor of this type of supernova is usually a red supergiant, but observations have shown that SN 1987A was caused by a compact blue supergiant. “It has been a mystery why the progenitor star was a blue supergiant,” says Masaomi Ono at the RIKEN Astrophysical Big Bang Laboratory.
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2020-03-15
Researches & Researchers
Possibilities of new science driven by deep learning - Masato Taki
The rapid development of AI is driven by technology called deep learning. However, no one knows yet why AI with high performance can be achieved through deep learning. We asked Masato Taki, who is working on deep learning in iTHEMS, about applied technology that extends from deep learning.
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2020-03-11
Announcement
Dr. Masato Taki wrote a Japanese article on the current stats of Deep Learning: "AI being Deceived" in Nikkei Science
Dr. Masato Taki (iTHEMS) wrote a Japanese article on the current stats of Deep Learning: "AI being Deceived" in Nikkei Science (Jan. 2020). This volume is in iTHEMS common room (246-248). Take a look it and enjoy his superb explanation on how AIs are fooled!
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2020-03-10
Award
Dr. Tomoki Ozawa received 11th annual RIKEN Research Incentive Award (Ohbu Award)
Tomoki Ozawa received "FY2019 Researcher Incentive Award (桜舞賞)" on March 10, 2020 for his achievements in the "Study of Geometric Effects in Synthetic Quantum Systems". Congratulations!
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2020-03-05
Press Release
New Hypernucleus "Xi-Tetrabaryon" -- Unravelling the behavior of Xi-particle by high-precision computations
An international research group including Dr. Tetsuo Hatsuda (Program Director, iTHEMS), and Takumi Doi (Senior Research Scientist, iTHEMS / Quantum Hadron Physics Laboratory, RIKEN) has theoretically predicted the existence of a new hyper-nucleus (hypernucleus), the Xi-Tetrabaryon, consisting of one Xi-particle and three nucleons. Please see the related link for details
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2020-02-26
Research News
New story released "Let's ask a RIKEN doctor!" (Written in Japanese)
"Let's ask a RIKEN doctor!" is a content that explains the forefront of RIKEN research for children in an easy-to-understand.
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2020-02-19
Research News
Modeling the insides of a neutron star -- Improvements to a model for the inside of a neutron star make it applicable to neutron star mergers
RIKEN astrophysicists have developed an improved model for the interior structure of neutron stars that agrees well with observations. Unlike previous models, it can be extended to consider what happens when two neutron stars merge. The collapsed remnants of giant stars, neutron stars are fascinating objects. They are a mere 20−30 kilometers in diameter but are nearly 400,000–600,000 times more massive than the Earth, which makes them incredibly dense. Neutron stars are not uniform agglomerations of neutrons—like the astrophysical equivalent of a giant atomic nucleus containing only neutrons. Rather they have an onion-like structure. Theorists have been busy trying to model this internal structure based on quantum mechanics and data from observations.
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2020-02-17
Seminar Report
Boosting the lensing study for DM properties with machine learning techniques
Strong lensing of the galaxy, which can be seen as arc-like features, is a powerful probe of the small-scale DM halos. The populations of small-scale DM halo give us hints about its particle properties. We need to manage huge parameter spaces (e.g. redshift distribution of the source galaxies, lensing galaxies, mass functions of perturbing subhalos and so on) to determine the subhalo signatures from the strong-lensing image data using likelihood ratio test. The machine-learning based techniques of the reduced likelihood ratio estimator enable us to derive the parameters of subhalo mass function, which are key quantities to access the nature of DM, in an efficient way. The importance of this technique increases for the coming era of large-sized lensing image data. In the near future, we should probe the parameters of the subhalo mass function hence the DM properties from galaxy-galaxy lensing. Furthermore, the method is so flexible that encourages us to consider much wider applications in DM search.
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2020-02-13
Seminar ReportBiology Talk by Dr. Yasuo Yasui, February 5, 2020.
On February 5, 2020, Dr. Yasuo Yasui, a plant geneticist from Kyoto University, gave a talk on his research on buckwheat (=soba) genetics. First, he explained how the current food supply of the world is heavily dependent on a very small number of plants, and that there is a pressing need to increase the yield of many other non-major crops, including buckwheat. He argued that now we have the tools to tackle this problem thanks to the advance in genome sequencing technologies, and that data science, computer science, and mathematical science have important roles to play. He then presented his previous research on buckwheat genetics and genomics, such as the identification of certain genes in buckwheat that are important for buckwheat breeding. He also showed some slides from field trips in South China (mainly Yunnan province) to collect wild buckwheat species, and explained his ongoing research in trying to understand the origin and domestication process of buckwheat, which is a joint effort with Jeffrey Fawcett from iTHEMS, and other researchers in Japan, China, and the UK. The talk was aimed at non-biologists, and many non-biologists from iTHEMS were able to join and ask many questions.
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2020-02-12
Seminar Report
Math Seminar Talk by Dr. Martin Skrodzki, February 7, 2020.
Dr. Martin Skrodzki, who stays at RIKEN iTHEMS as a postdoctoral researcher for the year 2020, gave a talk at the Math Seminar on February 7, 2020. The title of his talk was "Solved and open problems regarding the neighborhood grid data structure". He began with introducing the k-d tree for a finite set with coordinates in the plane and explained that by using this tree one can find the nearest point from a given point in a reasonable time. Then, he looked at the neighborhood grid data structure introduced by Joselli et al. in 2009, which is an n times n matrix filled by pairs of numbers (f(i,j),g(i,j)) where f and g are surjections to the set of numbers from 1 to n squared. He gave the definition of a stable state and explained that any grid data structure can be stabilized and that stabilization can be done in a short time using parallel computation. He explained the correspondence between a generic set of n squared points in the plane and stable grid data structures, and discussed several open questions around this correspondence. The talk was very accessible for everyone and the participants enjoyed it very much.
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2020-02-12
Researches & Researchers
Using genomic information to understand the evolution of species - Jeffrey Fawcett
Many people think of experiments when they hear the words “biological research.” However, Jeffrey Fawcett researches the evolution of species by analyzing genetic information using computers. Below, we will introduce some of his theoretical research.
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2020-02-06
Book
Quark-Gluon Plasma: From Big Bang to Little Bang
Author: Kohsuke Yagi, Tetsuo Hatsuda and Yasuo Miake Language: English Part of Cambridge Monographs on Particle Physics, Nuclear Physics and Cosmology
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2020-02-04
Hot Topic
Workshop on Communication for Interdisciplinary Collaboration
On January 28th, iTHEMS member Don Warren co-hosted a workshop on Communication for Interdisciplinary Collaboration. The goals of this workshop were (1) to learn how to communicate with people who do not study the same topic you do, and (2) to practice explaining your work so that a non-expert can decide if they want to join your project. The workshop was open to all RIKEN staff in all fields and positions, and turnout was very good: scientists from multiple centers attended, as did several non-research staff. Everyone who attended learned two key points to make cross-discipline communication easier and more productive. First, listen actively when someone is talking about their work to you; don’t fixate on the first interesting thing and stop listening to the rest of their explanation. Second, K.I.S.S.—keep it short and simple! (It is easy to talk about what to do, but it was much harder to practice it during the workshop.) The workshop facilitator was Christiane Brew, a performer and trainer who uses techniques from improvisation to encourage open discussion, deep listening, and clear “pitching”. This was the second of two workshops organized in FY2019 by Don and Amanda Alvarez of CBS. Support for the workshop came from the RIKEN Collaboration Seed fund. If this workshop is repeated next year, please consider joining and practicing your communication skills so you will be ready to start on your next interdisciplinary collaboration.
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2020-02-01
Book
Handbook of Astrophysics
Edited by Fumio Takahara et al. Language: Japanese
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2020-01-31
Hot Topic
Summary of interdisciplinary workshop "Present and Future of the Quantum Computing (QC)"
Interdisciplinary workshop "Present and Future of the Quantum Computing (QC)" hosted by MEXT and sponsored by iTHEMS and CEMS was held on Jan.29, 2020 at RIKEN Suzuki Umetaro Hall. There were more than 170 people got together from academia, industries and publishers. For the people who could not enter the hall, the talks were also broadcasted to the iTHEMS room 160. The scientific session was started with a review talk on the history of quantum-bit researches by Yasunobu Nakamura (CEMS). It was then followed by 11 talks which covered wide topics ranging from the QC architecture development to QC algorithms. The very last talk was given by our iTHEMS colleague, Jason Chang (iTHEMS/UCB), who discussed the adiabatic quantum computing and possible near-term engineering applications on the basis of his recent QC works. A poster session with about 30 posters from many different areas of science was also held with very lively discussions, especially among young researchers. Since the meeting was so successful to provide a platform for the researchers interested in this growing field of QC, we will definitely have the 2nd meeting in the near future.
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2020-01-31
Seminar Report
ABBL-iTHEMS Joint Seminar by Dr. Hajime Sotani
As ABBL/iTHEMS seminars, Dr. Hajime SOTANI gave a talk about "Neutron stars and nuclear saturation parameters" on 24th January. So far, many equations of state (EOSs) for neutron star matter are proposed, but the EOS is not fixed yet. This is mainly because the difficulty to obtain the information for high density region via terrestrial experiments. Thus, as an inverse problem, neutron stars are a suitable laboratory for probing the nuclear properties in the high density region. In this talk, it has been discussed the possibility for constraining the nuclear saturation parameters via the neutron star observations, especially focusing on the low-mass neutron stars. Any EOSs can be expanded in the vicinity of the saturation point as a function of the baryon number density, where the expansion coefficients correspond to the saturation parameters. So, each EOS has an own set of saturation parameters. Among the saturation parameters, the incompressibility (K0) for symmetric nuclear matter and the so-called slope parameter (L) for pure neutron matter are relatively difficult to constrain, because these are a kind of the derivative around the saturation point. Thus, in particular these two saturation parameters have been focused in this talk. In addition, the EOSs for high density region can not be expressed well only with the saturation parameters, but one may be able to discuss the EOSs with the saturation parameters up to twice the saturation density. In practice, by systematically examining the masses of low-mass neutron stars constructed with various EOSs up to twice the saturation density, the suitable combination of K0 and L for expressing well the low-mass neutron stars has been found successfully, i.e., eta^3 = (K0 * L^2). That is, the neutron star mass and gravitational redshift can be expressed well as a function of eta and the stellar central density. This is suggested that the value of eta and central density could be constrained via the simultaneous observations of neutron star mass and gravitational redshift. Furthermore, using eta, the possible maximum mass of neutron stars has been discussed together with the constraint obtained from the gravitational wave event, GW170817, and NICER observation.
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2020-01-30
Hot Topic
Farewell note from Dr. Tomoki Ozawa
Hello. My name is Tomoki Ozawa. I am a senior research scientist at RIKEN iTHEMS. As of February, I am leaving iTHEMS and moving to Advanced Institute for Materials Science (AIMR) in Tohoku University, Sendai, to start my own group as an associate professor. I joined iTHEMS on April 2018; I cannot believe that it has already been almost two years. Time really flies like an arrow. Before joining iTHEMS, my research career has been developed abroad (US, Italy, Belgium), and although I am a native of Japan, iTHEMS is the first Japanese affiliation I obtained as a researcher. Before coming back to Japan, I had always been worried if I could be accepted to the Japanese academic community. After joining iTHEMS, I learned that my worries were needless. I was surprised by the welcoming atmosphere of iTHEMS, and even though I was the only condensed matter physicist in iTHEMS, I could easily find somebody to discuss in the iTHEMS coffee room. What helped me even more to place myself in Japan were the various satellite offices of iTHEMS in (and also outside) Japan. These satellite offices made it easy for me to visit and know what is going on in various other places in Japan. After spending almost two years in iTHEMS, although I am still constantly surprised by cultural differences between Japan and other places I have been, I feel that I have comfortably become a part of the academic community in Japan. In terms of research, what was great being in iTHEMS was that I could do whatever research I wanted to do, without any pressure on the selection of topic or to report what I am doing to my boss. I really appreciated the academic freedom here. I am also starting to build collaborations in Japan. The new collaborations I am building are quite interdisciplinary (including atomic physics, photonics, and even biophysics), thanks to the wide scope of interests of people in iTHEMS. It has been a real pleasure to spend time in the beginning period of iTHEMS, and I am sure that iTHEMS will flourish even more in the coming years. AIMR has a satellite office of iTHEMS, and I expect to maintain active interactions with iTHEMS after I move to AIMR. I will also most likely come to iTHEMS offices (perhaps the coffee room in Wako) from time to time, and I am looking forward to seeing the successful development of iTHEMS in the future.
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2020-01-27
Hot Topic
Search for gamma-ray signals from dark matter annihilations in extended dwarf spheroidal galaxies, article on the Astronomical Herald
The importance of the dark matter density distribution in target galaxies is discussed under realistic settings of the future gamma-ray experiment.
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2020-01-24
Seminar Report
Math seminar by Dr. Shu Nakamura
The iTHEMS Math seminar was held on 23 January, inviting Shu Nakamura from Gakushuin university. The title of the talk was “Semiclassical methods in mathematical quantum mechanics”. The topic was semiclassical analysis and scattering theory of Schrödinger operators. In the first part, the speaker gave a introductory talk on the microlocal analysis and semiclassical analysis of Schrödinger operators. He started his talk by introducing a canonical quantization. Then he explained how canonical quantization is understood in the framework of semiclassical and microlocal analysis. Moreover he explained some recent results on this research field. In the second part, the speaker explained his recent results on scattering matrix of Schrodinger operators with long range potentials. At the beginning, he introduced the definition of scattering matrix and some known results. Then he stated his main result on the representation of scattering matrix. As an application, he gave some examples of long range potentials for which he proved several spectral properties of scattering matrix.
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2020-01-24
Featured Paper of the Week
Distance between collapsing matter and trapping horizon in evaporating black holes
How deep can an apple fall into the horizon of a black hole? Of course, in the case of a classic black hole, the apple reaches the center. However, the real world is described by quantum theory, and black holes evaporate by Hawking radiation. This changes the fate of the apple. Negative energy due to vacuum quantum fluctuations is generated near black holes, which enters the black holes and reduces their energy. If there is a horizon, the negative energy will make the horizon smaller. Then, the horizon becomes timelike (while it is null in the classical case). In this paper, we solved approximately the Einstein equation in the vicinity of the horizon and examined the physical (proper) distance between the falling apple and the horizon. It turned out that the distance is a few of the Planck length (due to the exponentially delayed time inside the horizon). This means that essentially no apples fall into the black hole. This result suggest that we should reconsider whether the black hole really has a horizon.
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2020-01-23
Person of the Week
Self-introduction: Martin Skrodzki
My name is Martin Skrodzki and I was born in Germany. I studied computer science and mathematics from 2008 to 2011 at TU Dortmund University in Germany where I obtained two Bachelor's degrees. Afterwards, I spend two terms on a Fulbright travel grant at the Texas A&M International University in Laredo, Texas, USA continuing with graduate studies in mathematics. I finishes these with a Master's degree at Freie Universität Berlin, Germany in 2014. My focus in the coursework and in my Master's thesis was on discrete geometry and discrete mathematics. In early 2015, I started work on my PhD with Prof. Polthier at Freie Universität Berlin in the group "Mathematical Geometry Processing". My thesis, titled "Neighborhood Data Structures, Manifold Properties, and Processing of Point Set Surfaces" covers three topics all centered in the context of point set processing. Please find the thesis via the link shown below. I graduated with the title of "Dr. rer. nat" (doctor of the natural sciences) in July 2019. Immediately after my graduation, I started a first postdoc at the Institute of Computational and Experimental Research in Mathematics (ICERM), Brown University, Providence, RI, USA. The position was part of the topical semester program "Illustrating Mathematics" which was concerned about finding new, exciting visualizations of mathematical structures and objects, see the link shown below for some of the results obtained. My research interests are set between computer science and mathematics. I am currently very interested in visualization of high-dimensional data via dimension-reduction methods. Memberships in the Society of Applied and Industrial Mathematics (SIAM), the Solid Modeling Association (SMA), and Eurographics (EG) form my professional network. Finally, I am also an associate editor of the Journal of Mathematics and the Arts (JMA).
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2020-01-17
Seminar Report
Math Seminar by Prof. Syuji Yamamoto
The iTHEMS Math seminar was held on 17 December, inviting Shuji Yamamoto from Keio university. The title of the talk was “Multiple Zeta Values: Interrelation of Series and Integrals”. The topic was multiple zeta values (MZVs), which is a generalization of the values of the Riemann zeta function. In the first part, the speaker explained the definition of MZVs, and the statement of the Zagier conjecture, which predicts how many algebraic relations should exist among MZVs. Moreover, he explained several known algebraic relations, including Euler relation, Hoffman relation, duality, sum formula, Ohno relation, etc. He also provided two types of proof of duality, one of which is due to himself and Seki. In the second part, the speaker explained Double Shuffle Relation and Regularization. It is conjectured that these relations generate all the algebraic relations of MZVs, but this is a hard open problem. For example, it is unknown whether the relations imply duality. However, many relations are generated by these relations. The speaker explained some concrete examples, after introducing integral series identity.
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2020-01-16
Person of the Week
Self-introduction: Hajime Sotani
Understanding neutron star physics is my research topic. Neutron star is provided via supernova explosion, which happens at the last moment of life of massive star. Neutron star is a unique laboratory for understanding the physics in extreme states. In fact, the density inside the neutron star significantly exceeds the nuclear standard density and the magnetic and gravitational fields around/inside the star become much stronger than those observed in our solar system. So, as an inverse problem, one could extract some aspects of physics in such extreme states via the observation of neutron star itself and/or the phenomena associated with neutron stars. For this purpose, (gravitational wave) asteroseismology is a powerful technique, which is similar to seismology in Earth and helioseismology in Sun. With this approach, we are trying to extract the "invisible" neutron star properties. Since our research is not only in astrophysics but also strongly associated with nuclear physics and condensed matter physics, I am very happy if I can make an interdisciplinary collaboration with the members of iTHEMS for solving a problem in neutron stars.
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2020-01-09
Featured Paper of the Week
Akizuki-Nakano vanishing theorem and its application for globally F-split 3-folds
In algebraic geometry, it is important to study spaces (=varieties) which may admit singular points. "Smoothing" is an effective way to deal with singularities. Roughly speaking, a smoothing of a (singular) variety helps us to find another variety which is non-singular and is "similar" to the original variety. Namikawa proved that a complex Fano 3-fold whose singular points are at worst ordinary double points admits a smoothing. In this paper, we give an analogy of this result in the case where the Fano variety is not complex, but is defined over a field of positive characteristic. The key ingredient of the proof is the vanishing of the second cohomology of the tangent space, which is a vector space containing an obstruction to construct a smoothing. We prove a positive characteristic analogue of the Akizuki-Nakano type vanishing for 3-dimensional varieties and as a corollary, we conclude the result about a smoothing.
187 news in 2020