Seminar
385 events

Seminar
Several identities related to the degenerate Bernoulli polynomials and numbers
February 24 (Sat) at 16:00  17:00, 2018
Prof. Takao Komatsu (Professor, Wuhan University, China)
In this talk we demonstrate some relations in degenerate Bernoulli polynomials, which may be expressed as a general convolution identity. We also show some properties of hypergeometric degenerate Bernoulli polynomials and numbers.
Venue: Seminar Room #160
Event Official Language: English

Seminar
Diophantine Frobenius Problems — counting theory, generating function and zeta functions
February 23 (Fri) at 16:00  17:00, 2018
Prof. Takao Komatsu (Professor, Wuhan University, China)
When a_1, ...,a_m are relatively prime positive integers, the number of solutions of the linear Diophantine equation a_1 x_1 + … + a_m x_m = b in nonnegative integers x_1, ...,x_m, for any integer b, is our concern. We show several formulas to give the largest integer b without solution. Then we discuss the generating function of the number of solutions. Finally, we derive an explicit expression for an inverse power series over the gaps values of numerical semigroups generated by two integers. It implies a set of new identities for the Hurwitz zeta function.
Venue: Seminar Room #160
Event Official Language: English

Statistical mechanics of tissue homeostasis
January 22 (Mon) at 14:00  15:00, 2018
Dr. Kyogo Kawaguchi (The University of Tokyo)
Adult tissues undergo rapid turnover as mature cells are continuously lost and new cells arise through cell division. The balance between the gain and loss of cells must be finely orchestrated to maintain tissues, but how this balance is achieved remains largely unknown. Previous works [1] have used universal scaling laws to claim that the fate choice of stem cells (division or differentiation) are made strictly cellautonomously. However, we recently recorded every stem cell fate choice within the mouse skin epidermal regions over one week and found that, far from being cellautonomous, stem cell loss by differentiation is compensated by direct neighboring division [2]. In this talk, I will describe a model of tissue homeostasis using a macroscopic nonequilibrium setup, and explain how the coarsegraining of this model will lead to the effective dynamics of the voter model (DP2). I will show how we can use the property of dynamical crossover in the model from the cellautonomous regime (critical birthdeath model) to the fatecoordinated regime (voter model) to measure the length and time scales of stem cell coordination. I will then explain the pitfall in twodimensions of using scaling relations for the clonal fate trace of cells, and present the workaround we used in the data analysis to definitively show the existence of celltocell fate correlation.
Venue: Common Room #246248
Event Official Language: English

Compactstar phenomena and equation of state
December 28 (Thu) at 10:30  11:30, 2017
Dr. Shun Furusawa (Special Postdoctoral Researcher, iTHEMS)
Venue: SUURICOOL (Kyoto)
Event Official Language: English

Theoretical study on the universality in biological clock and its speciesspecificity
December 27 (Wed) at 16:00  17:00, 2017
Dr. Gen Kurosawa (Research Scientist, iTHEMS / Research Scientist, Theoretical Biology Laboratory, RIKEN)
Venue: SUURICOOL (Kyoto)
Event Official Language: English

Mathematical Modeling of Retinal Cellular Mosaic Pattern Formation
December 27 (Wed) at 13:30  14:30, 2017
Dr. Noriaki Ogawa (Postdoctoral Researcher, Interdisciplinary Theoretical Science Research Group (iTHES), RIKEN)
Venue: SUURICOOL (Kyoto)
Event Official Language: English

Topology of linear operators and topological insulators
December 27 (Wed) at 10:30  11:30, 2017
Dr. Yosuke Kubota (Research Scientist, iTHEMS)
Venue: SUURICOOL (Kyoto)
Event Official Language: English

Chiral Phases in Frustrated 2D Antiferromagnets and Fractional Chern Insulators
December 21 (Thu) at 11:00  12:00, 2017
Prof. Eduardo Fradkin (University of Illinois, USA)
Venue: #535537, 5F, Main Research Building
Event Official Language: English

Seminar
Baryon Asymmetry of the Universe generated by Helical Hypermagnetic fields through chiral anomaly
December 20 (Wed) at 11:00  12:00, 2017
Dr. Kohei Kamada (Center for Theoretical Physics of the Universe, Institute for Basic Science, Republic of Korea)
Recent observations of TeV blazars by Fermi identified deficits of secondary GeV cascade photons.These observations can be explained by intergalactic magnetic fields, which may have a primordial origin.If the magnetic fields are helical and generated before the electroweak symmetry breaking,nontrivial interaction between (hyper)magnetic fields and other particles can cause some interestingand non negligible phenomena in the early Universe. In this talk, I will show that the baryon asymmetry can be generated by the chiral anomaly and this mechanism might be responsible for the present baryon asymmetry of the Universe. The intergalactic magnetic fields are its smokinggun. If this mechanism is responsible for the present Universe,the BSM physics is needed for the generation of (hyper)magnetic fields but not for the baryogenesis.
Venue: Seminar Room #160
Event Official Language: English

Seminar
A New Look at Matrix Models for QCD3
November 24 (Fri) at 16:30  18:00, 2017
Dr. Takuya Kanazawa
Nonchiral random matrix models for QCD in 2+1 dimensions and their new generalizations will be discussed.
Venue: Seminar Room #160
Event Official Language: English

The RiemannRoch theorem
September 26 (Tue) at 14:00  15:00, 2017
Dr. Yosuke Kubota (Research Scientist, iTHEMS)
In the mid 19th century, B. Riemann introduced the notion of Riemann surface in his Ph.D thesis on complex analysis. Together with nonEuclidean geometry, the theory of Riemann surface is a germination of modern geometry in both algebraic and analytic sense. In this talk, I will give an introduction of the theory of Riemann surface centering around the RiemannRoch theorem. It is an important prototype of the AtiyahSinger index theorem, the starting point of my research field.
Venue: Seminar Room #160
Event Official Language: English

Seminar
Connections of Pair Correlations to Equidistribution and Additive Energy
August 31 (Thu) at 13:30  15:00, 2017
Dr. Thomas Lachmann (Graz University of Technology, Austria)
Venue: Common Room #246248
Event Official Language: English

Seminar
Pulsar Winds: Ultimate Relativistic Outflows
August 29 (Tue) at 13:30  14:30, 2017
Dr. Dmitry Khangulyan (Rikkyo University)
A highest density body that features the strongest magnetic field launches, no surprise, an ultimate outflow  pulsar wind. Despite their relativistic nature and complexity, a few simple analogies can help us to understand the essence of pulsar physics. I will present several links connecting basic mechanics and electrodynamics, everyday thermodynamics and hydrodynamics to the processes taking place in the vicinity of pulsars. These fundamental relations not only provide a simple mental image for the pulsar physics but also have their imprint in highenergy data obtained from pulsars and pulsar wind nebulae.
Venue: #433, Main Research Building
Event Official Language: English

Seminar
Joint Seminar with Condensed Matter Theory Laboratory
July 20 (Thu) at 13:30  15:00, 2017
Dr. Shinsei Ryu (The University of Chicago, USA)
Venue: #435437, Main Research Building
Event Official Language: English

An invitation to number theory
July 10 (Mon) at 13:30  14:30, 2017
Dr. Hiroyasu Miyazaki
The goal of number theory is to reveal the mystery of natural numbers 1,2,3…. It has a long history, and it is still developing by exchanging ideas with many other branches of mathematics. In the long history, number theory had been thought of as a pure mathematics with no direct application outside mathematics. However, the rapid development of computer science changed the situation: the theory of prime numbers has been applied to code theory, cryptography, random number generation etc. It seems that there are several researches in physics and biology using the method of number theory, too. The aim of this talk is to give a beginnerfriendly introduction to number theory. Among many topics, I will focus on very fundamental and important concepts: the “padic numbers” and the “finite fields.” I hope that this talk will motivate you to relate your research to number theory.
Venue: Seminar Room #160
Event Official Language: English

Seminar
Braids and topological mixing
June 26 (Mon) at 14:00  15:00, 2017
Dr. Eiko Kin (Osaka University)
In mathematics, the braids are important tools for the knot theory, hyperbolic geometry, and dynamical systems etc. In the last ten years, the braids have been used to study mixing in fluids. Various simple mixing devices (e.g. taffy machines) have been developed. These devices utilize a particular type of braid, socalled a pseudoAnosov type. The notion of pseudoAnosov braids comes from the NielsenThurston theory on the surface automorphisms, and the theory says that the devices using pseudoAnosov braids are "efficient" in some sense. In this lecture, I will give a quick introduction of the NielsenThurston theory and the classification of braids. I will give a picture of the "complexity" forced by pseudoAnosov braids. In particular, I will explain why pseudoAnosov braids are useful and why they can be used to build interesting mixing devices. Cosponsored by RIKEN iTHEMS and AIP Mathematical Science Team
Venue: RIKEN Tokyo Liaison Office (Nihonbashi)
Event Official Language: English

Homological algebra, Renormalization and Transversality
June 26 (Mon) at 10:30  11:30, 2017
Prof. Kenji Fukaya (Permanent Member, Simons Center for Geometry and Physics, Stony Brook University, New York, USA)
Transversality is a basic concept of differential topology and theory of manifold. Homological algebra may be regarded as a method to approximate `spaces' by an algebra and is a basic concept in agebraic topology. I would like to explain in this talk how they are related to some basic problem of quantum field theory such as renormalization. Cosponsored by RIKEN iTHEMS and AIP Mathematical Science Team
Venue: RIKEN Tokyo Liaison Office (Nihonbashi)
Event Official Language: English

Galois representations and the Langlands correspondence
June 8 (Thu) at 13:30  14:30, 2017
Dr. Kazuki Tokimoto (Kyoto University)
The Langlands correspondence relates numbertheoretic objects to completely different objects. While still largely conjectural, it has attracted interests of many mathematicians over the years. It is known that the local Langlands correspondence in a special case can be constructed in a geometric way (the nonabelian LubinTate theory). In this talk, I will explain some basic concepts in mathematics (such as groups, representations and Galois groups) and then try to convey some flavor of my result related to the nonabelian LubinTate theory.
Venue: Seminar Room #160
Event Official Language: English

Atypicality of most fewbody observables
May 29 (Mon) at 13:30  14:30, 2017
Dr. Ryusuke Hamazaki (The University of Tokyo)
Understanding how isolated quantum systems thermalize has recently gathered renewed interest among theorists, thanks to the experimental realizations of such systems. The eigenstate thermalization hypothesis (ETH) is particularly investigated as a sufficient condition for the approach to thermal equilibrium. It states that diagonal matrix elements of an observable for the energy eigenstates are almost the same within a small energy shell. The ETH is justified for an observable and a Hamiltonian whose respective eigenbases are typically oriented to each other; i.e., for almost all unitary transformations of these two eigenbases with respect to the uniform Haar measure. In this seminar, we consider a Hamiltonian with fewbody interactions and random observables without assuming the uniform Haar measure. These observables are chosen in an operational manner as random linear combinations of the operator basis of spins. We show that most fewbody observables have atypical matrix elements when the energy width is not exponentially small with the system size. Namely, the maximum fluctuation for diagonal matrix elements is larger than that predicted by the uniform Haar measure.
Venue: #433, Main Research Building
Event Official Language: English

Seminar
Guiding principles to develop tough polymer materials: An exactly solvable model
May 25 (Thu) at 10:30  11:30, 2017
Dr. Naoyuki Sakumichi (Ochanomizu University)
Needs to impart appropriate elasticity and high toughness to viscoelastic polymer materials are ubiquitous in industries such as concerning automobiles and medical devices. One of the major problems to overcome for toughening is catastrophic failure linked to a velocity jump [13], i.e., a sharp transition in the velocity of crack propagation occurred in a narrow range of the applied load. However, its physical origin has remained an enigma despite previous studies [4] over 35 years. Here, we propose an exactly solvable model that exhibits the velocity jump incorporating linear viscoelasticity with a cutoff length for a continuum description [5]. With the exact solution, we elucidate the physical origin of the velocity jump: it emerges from a dynamic glass transition in the vicinity of the propagating crack tip. We further quantify the velocity jump together with slow and fastvelocity regimes of crack propagation, which would stimulate the development of tough polymer materials.
Venue: Seminar Room #160
Event Official Language: English
385 events
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