Guiding principles to develop tough polymer materials: An exactly solvable model

May 25 (Thu) at 10:30 - 11:30, 2017

Naoyuki Sakumichi (Project Assistant Professor, Soft Matter Center, 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 [1-3], 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 fast-velocity regimes of crack propagation, which would stimulate the development of tough polymer materials.

Venue: Seminar Room #160

Event Official Language: English

Shapes of discrete groups

May 18 (Thu) at 15:30 - 17:00, 2017

Takashi Tsuboi (Deputy Program Director, iTHEMS)

The 21st iTHES Theoretical Science Colloquium I will talk about several attempts to understand infinite groups. The group structure appears almost everywhere in mathematics. Groups describe the symmetry of mathematical objects. A discrete group is a space with usually countably many points which is not an interesting topological space. But people began distinguishing shapes of different groups. For example, the free group on two generators and the free abelian group of rank two should have different shapes. One may think that the shape of the free group on two generators is infinite four valent tree while the shape of the free abelian group of rank two is the lattice on the Euclidean plane. The idea of geometric group theory has been developed to describe the properties of discrete groups. For a finitely presented group, Gromov defined the hyperbolicity of it by looking at its Cayley graph and showed that the hyperbolic groups have many nice properties and it looks like free groups. When we need to investigate groups, first we may look at its abelianization, and then, for example, we may look at its nilpotent approximation. If its abelianization is the trivial group, however, then we should find another way. In this case, we have the commutator length function on the group. Bavard established the notion of stable commutator length and relate it to the space of homogeneous quasimorphisms. We can also look at the conjugation invariant norms. My interest on these invariants came from the study on diffeomorphism groups of manifolds. The identity connected components of diffeomorphism groups of compact connected manifolds have been known to be simple. I could show that for manifolds of dimensions other than 2 and 4, the commutator length function is bounded. There are many interesting infinite simple groups with unbounded commutator length functions, and it would be very interesting to find new methods to describe their shapes.

Venue: Suzuki Umetaro Hall

Event Official Language: English

Deep learning primer for physicists and astronomers

May 10 (Wed) at 13:30 - 17:30, 2017

Venue: Nishina Hall

Event Official Language: Japanese

Chaos, Quark, Black Hole

April 14 (Fri) at 14:30 - 15:30, 2017

Koji Hashimoto (Professor, Department of Physics, Osaka University)

Venue: Seminar Room #160

Event Official Language: English

General Relativity and Gravitational Waves

April 13 (Thu) at 15:00 - 16:30, 2017

Takahiro Tanaka (Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

The 20th iTHES Theoretical Science Colloquium A hundred years have passed since general relativity was proposed by A. Einstein. This beautiful theory passed all experimental tests so far but almost always in a week gravity regime where perturbative expansion around flat spacetime gives a good approximation. Recent direct detection of gravitational waves by LIGO opened up a new window to test general relativity in a strong gravity regime. At the same time, cosmological observations are getting more and more accurate, which also gives a ground to test the validity of general relativity. I'd like to discuss the progress of this area in the past and what will happen in near future.

Venue: Okochi Hall

Event Official Language: English

HPC in precision medicine

April 11 (Tue) at 15:30 - 16:30, 2017

Tilo Wettig (Professor, Universität Regensburg, Germany)

In theoretical particle physics we have been using high-performance computing (HPC) for three decades to make scientific progress. Recent advances in next-generation sequencing, as well as the corresponding bioinformatics questions, generate an obvious need for HPC methods in the field of precision medicine. We have recently started to explore this field and believe that our HPC expertise can be used to speed up time-critical workflows, to better manage the large amount of data involved, and to lead to more cost- and energy-efficient solutions. I will discuss a few concrete examples, including interesting questions in single-cell sequencing.

Venue: #433, Main Research Building

Event Official Language: English

Geometry in condensed matter physics

April 8 (Sat) at 13:00 - 14:00, 2017

Naoto Nagaosa (Deputy Director, Group Director, Strong Correlation Theory Research Group, RIKEN Center for Emergent Matter Science (CEMS) / Professor, Department of Applied Physics, Graduate School of Engineering, The University of Tokyo)

Quantum geometry plays essential roles current condensed matter physics. Aharonov-Bohm effect and Berry phase as its generalization are the key concepts in electronic systems in solids, which are described by the Bloch wavefunctions and electron correlation effects on top of them. In this talk, I will describe how the geometry determines the physical properties of materials focising on the gauge structure and electomagnetic responses.

Venue: Seminar Room #160

Event Official Language: English

The local time of simple random walks and Gaussian free fields in two dimensions

April 6 (Thu) at 10:30 - 11:30, 2017

Izumi Okada

By using the method of probability analysis, we have researched the local time of a multidimensional-simple random walk. Note that the local time means the number of visits of a simple random walk to specific points in integer lattice. It is known that functionals of a local time and Gaussian free fields denote a variety of nonlinear and mathematical phenomena such as random media. Then, we are observing the relationship between two processes. As a first step, we especially observe favorite points (the singular sites where the local time is large) et al. By A.Dembo, Y.Peres, O.Zeitouni, J.Rosen, who are leading experts in this field, the importance of this point has been recently shown.

Venue: Seminar Room #160

Event Official Language: English

Fatgraph models for RNA molecules

March 23 (Thu) at 10:30 - 11:30, 2017

Hiroyuki Fuji (Associate Professor, Faculty of Education, Kagawa University)

Concepts of fatgraphs and partial chord diagrams occur in many branches of mathematics, including topology, geometry, and representation theory. During the last decade, some applications of these mathematical objects to the research of the molecular biology have been reported. Among them, in particular, a characterization by the genus in the fatgraph presentation of the RNA has been studied remarkably. In this talk, I will explain how the concepts of fatgraphs and partial chord diagrams are applied to the study of the secondary structure of the RNA with pseudoknots, and introduce the matrix model that is invented by basic techniques of the quantum field theory. If time permits, I shall discuss about the matrix model of the protein, and speculate about further developments.

Venue: Seminar Room #160

Event Official Language: English

iTHES Kobe Workshop

March 4 (Sat) at 10:00 - 18:10, 2017

This workshop is partially supported by iTHEMS.

Venue: Integrated Innovation Building (IIB)

Event Official Language: English

Application of Quantum Beam for Eco-tire Development

February 23 (Thu) at 15:00 - 17:00, 2017

Hiroyuki Kishimoto (Sumitomo Rubber Industries, Ltd.)

The 13th iTHES Academic-Industrial Innovation Lecture

Venue: Okochi Hall

Event Official Language: Japanese

Integrated Research Center of Kobe University

February 23 (Thu) - 24 (Fri), 2017

Venue: Integrated Research Center of Kobe University

Event Official Language: English

Quantum computing by quantum annealing

January 27 (Fri) at 15:00 - 16:30, 2017

Hidetoshi Nishimori (Professor, Tokyo Institute of Technology)

The 19th iTHES Theoretical Science Colloquium Quantum annealing is a generic platform to solve a class of computational problems using quantum mechanical effects. D-Wave Systems in Canada has built hardware to realize quantum annealing and has sold several of their machine to Google, NASA, Los Alamos National Laboratory, and Lockheed-Martin, which raised a good amount of interest not just from scientific communities but also from a wider public. In this talk, I will explain the basic theoretical framework of quantum annealing, overview the current status of hardware and theoretical developments, and discuss its impact on the society in general.

Venue: Okochi Hall

Event Official Language: English