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| 日時： | 2021年8月10日（火）15:00-16:00 |
| 場所： | オンライン開催 |
| 講演： | 物理ゲルの構造、弾性、振動特性：分子動力学シミュレーションを用いた研究 |
| Prof. Hideyuki Mizuno (Graduate School of Arts and Sciences, The University of Tokyo, Japan) 水野 英如 助教 （東京大学 大学院総合文化研究科 広域科学専攻） | |
今回の講演会はWeb会議ツールZoomを利用して開催します．
講演聴講をご希望の方は下記フォームへの記入・送信をお願いします．記入いただいたメールアドレス宛に講演聴講のためのZoomのミーティングURLおよびパスワードが送信されます．
| 日時： | 2020年12月16日（水） 16:15-17:15 |
| 場所： | オンライン開催 |
| 講演： | Recent Developments of Nonequilibrium Thermodynamic Theories of Gases |
| Prof. Takashi Arima (Department of Engineering for Innovation, National Institute of Technology, Tomakomai College, Japan) 有馬 隆司 准教授 （苫小牧工業高等専門学校 創造工学科 総合自然科学系） |
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| 要旨： | Nonequilibrium thermodynamic theories of continuous media of which applicable range goes beyond the local thermodynamic equilibrium have been developed. Starting from the pioneering works of Grad in the context of kinetic theory, of Cattaneo for a rigid heat conductor, and of Müller for the first phenomenological version of extended thermodynamics, several attempts have been made, for example, Rational Extended Thermodynamics, Extended Irreversible Thermodynamics, General Equation for the Nonequilibrium Reversible–Irreversible Coupling, the regularized moment approach, and others. In this talk, we present the state of the art on these modern nonequilibrium theories focusing on Rational Extended Thermodynamics. In particular, we consider rarefied gases and discuss the linkage with the kinetic theory. Conceptual discussions of the differences among these nonequilibrium theories are also summarized. |
今回の講演会はWeb会議ツールZoomを利用して開催します．
講演聴講をご希望の方は下記フォームへの記入・送信をお願いします．記入いただいたメールアドレス宛に講演聴講のためのZoomのミーティングURLおよびパスワードが送信されます．
| 日時： | 2020年11月27日（金） 16:15-17:15 |
| 場所： | オンライン開催 |
| 講演： | Some formulations of the volume force in the immersed boundary method and a new approach in combination with the lattice Boltzmann method |
| Prof. Kosuke Suzuki (Institute of Engineering, Academic Assembly, Shinshu University, Japan) 鈴木 康祐 准教授 （信州大学 学術研究院 (工学系) ） |
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| 要旨： | One of the important issues in computational fluid dynamics is to simulate moving-boundary flows efficiently. The immersed boundary method (IBM), which was proposed by Peskin in 1970s in order to simulate blood flows in the heart, has been reconsidered as an efficient method for simulating moving-boundary flows on a fixed Cartesian grid. In the IBM, it is assumed that the boundary is regarded as an infinitely thin shell, an incompressible viscous fluid fills in both inside and outside of the boundary, and the no-slip condition on the boundary is satisfied by volume force applied only near the boundary. The way to determine the volume force is the key concept of the IBM. In this talk, I introduce some formulations of the volume force in the IBM. Then, I present a new approach in combination with the lattice Boltzmann method (LBM). In this approach, the volume force of the IBM is regarded as the discontinuity of the stress tensor, and the stress tensor is calculated from the desired particle distribution functions of the LBM. This approach enables us to calculate the stress tensor on the boundary which is blurred by the volume force. |
今回の講演会はWeb会議ツールZoomを利用して開催します．
講演聴講をご希望の方は下記フォームへの記入・送信をお願いします．記入いただいたメールアドレス宛に講演聴講のためのZoomのミーティングURLおよびパスワードが送信されます．
| 日時： | 2020年7月22日（水） 15:00-16:00 |
| 場所： | オンライン開催 |
| 講演： | Mathematical Analysis of Moving Boundary Problems in the Kinetic Theory of Gases （分子気体力学における移動境界問題の数学解析） |
| Dr. Kai Koike (Department of Aeronautics and Astronautics, Graduate School of Engineering, Kyoto University, Japan) 小池 開 氏 （日本学術振興会 特別研究員(PD)） |
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| 要旨： | Moving boundary problems for kinetic equations have become an active area of research mainly due to its importance in MEMS applications. It has also proved to be a source of interesting mathematical problems. Despite this, it’s mathematical theory has not developed to a satisfactory level although there are some recent progresses. In this talk, I would like to review these results hoping to stir interaction between the engeneering and the mathematical community further, which has always been an important element in this field. |
| 日時： | 2019年12月19日（木）16:15-17:15 |
| 場所： | 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟）3階 b3n03室（航空宇宙工学専攻会議室） |
| 講演： | Solid-state physics of glasses |
| Hideyuki Mizuno, PhD (Graduate School of Arts and Sciences, The University of Tokyo, Japan) 水野 英如 助教 （東京大学 大学院総合文化研究科 広域科学専攻） |
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| 要旨： | In our lives, there are two types of solid-states materials. One is crystals, and the other is noncrystalline, glasses. We already have a good level of understanding of crystals. Their thermal and transport properties can be described in terms of phonons; their heat capacity and thermal conductivity are well described by the Debye theory and the phonon-gas theory, respectively. By contrast, we have only a limited understanding of glasses that exhibit fundamentally different properties from those of crystals. Because glasses are materials commonly encountered in our daily lives and are widely employed in modern technologies (examples include silicate glasses, metallic glasses, plastic materials, ceramics, and many other rigid, disordered materials), their understanding is crucial not only in physics and materials science but also in engineering. In this seminar, I would introduce the latest progress in understanding of glasses. |
普段とは違い，場所は吉田キャンパスです．ご注意ください．
| 日時： | 2019年11月1日（金）16:30-17:30 |
| 場所： | 京都大学 吉田キャンパス 工学部総合校舎 111講義室 |
| 講演： | On the homogenization problem for the linear Boltzmann equation |
| Prof. Francesco Salvarani (Léonard de Vinci School of Engineers, France & Dipartimento di Matematica, Università di Pavia, Italy) | |
| 要旨： | In this talk, we study the homogenization problem for the linear Boltzmann equation when the optical parameters are highly heterogeneous in the energy variable. We employ the method of two-scale convergence to arrive at the homogenization result. In doing so, we show the induction of a memory effect in the homogenization limit and we discuss its link with the self-shielding effect in nuclear reactor physics. The results presented here have been obtained in collaboration with Harsha Hutridurga and Olga Mula. |
| 日時： | 2019年7月23日（火）16:15-17:15 |
| 場所： | 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟）3階 b3n03室（航空宇宙工学専攻会議室） |
| 講演： | Compressible fluid approximation for rarefied gases in bounded domains |
| Prof. Renjun Duan (Department of Mathematics, The Chinese University of Hong Kong, Hong Kong) | |
| 要旨： | In this talk I will talk about two recent results on the mathematical justification of the compressible viscous fluid approximation of solutions to the Boltzmann equation in bounded domains when the Knudsen number is small. The first result is concerned with the situation where the diffusive reflection boundary condition is considered and the fluid equations are solved under the non-slip boundary conditions. The second result is focused on a specific case of the one-dimensional heat transfer for a steady rarefied gas flow between two parallel plates with diffusive reflection boundaries of different temperatures where the temperature difference is small but does not depend on the Knudsen number, and we show the existence of steady solutions by taking the approximation of fluid equations with slip boundaries together with the Knudsen layer equations. |
| 日時： | 2019年5月14日（火）16:15-17:15 |
| 場所： | 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟）3階 b3n03室（航空宇宙工学専攻会議室） |
| 講演： | The Mpemba and Kovacs effects in granular gases |
| Prof. Andrés Santos (Department of Physics, Universidad de Extremadura, Spain) | |
| 要旨： | Experimental observations reveal that the response to an excitation in a complex condensed matter system may depend on the entire system’s history, and not just on the instantaneous value of the macroscopic state variables. These memory effects signal the breakdown of the macroscopic description. Some typical memory effects include shape memory in polymers, aging and rejuvenation in spin glasses, active matter, and granular gases. In this talk I will focus on the last class of systems and consider two prototypical memory phenomena: the Mpemba and Kovacs effects. The Mpemba effect is a counterintuitive phenomenon according to which, given two samples of fluid, the initially hotter one may cool more rapidly than the initially cooler one. In the Kovacs effect, a system relaxing to a low temperature is suddenly put in contact with a reservoir at the same temperature as the instantaneous value the system has after a given waiting time; however, the system’s temperature does not remain constant but exhibits a nonmonotonic evolution before reaching its asymptotic steady value. Both the Mpemba and Kovacs effects in granular gases will be addressed by minimal descriptions based on kinetic theory, the theoretical predictions being numerically confirmed by the direct simulation Monte Carlo method and by event-driven molecular dynamics. |
| 日時： | 2019年1月18日（金） 16:30-17:30 |
| 場所： | 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟） 3階 b3n03室（航空宇宙工学専攻会議室） |
| 講演： | Data-driven modelling of dynamical system based on delay-embedding |
| Prof. Naoto Nakano (Center for Innovative Research and Education in Data Science, Institute for Liberal Arts and Sciences & Graduate School of Science, Kyoto University, Japan) 中野 直人 講師 （京都大学 国際高等教育院附属データ科学イノベーション教育研究センターおよび理学研究科） |
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| 要旨： | Delay embedding is well-known for non-linear time-series analysis, and it is used in several research fields such as physics, informatics, neuroscience and so forth. The celebrated theorem of Takens (1981) ensures validity of the delay embedding analysis: embedded data preserves topological properties which the original dynamics possesses. This method is easy to implement for time-series analysis, however, resultant embedded dataset may easily vary with the delay width and the delay dimension, namely, “the way of embedding”. In a practical sense, this sensitivity may sometimes interfere with users’interpretation of embedded objects. In this study, to derive an appropriate embedding Ansatz, we investigate the mathematical structure of delay-embedding from a view point of linear operator theory. In this talk, we will briefly overview its framework, and we will show some numerical results of time-series analysis by the present method. For example, prediction, attractor reconstruction, causality detection and control problems. |
| 日時： | 平成30年8月24日（金） 15:00-17:00 |
| 場所： | 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟） 3階 b3n03室（航空宇宙工学専攻会議室） |
| 講演1： | Entropy methods and cross-diffusion systems: derivation and entropy structure |
| Prof. Ansgar Jüngel (Institute for Analysis and Scientific Computing, Vienna University of Technology, Austria) |
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| 要旨1： | Nature is dominated by systems composed of many individuals, belonging to various species, with a collective behavior. Instead of calculating the trajectories of all individuals, it is computationally much simpler to describe the dynamics of the individuals on a macroscopic level by averaged quantities such as population densities. This leads to systems of highly nonlinear partial differential equations with cross diffusion, which may reveal surprising effects such as uphill diffusion and diffusion-induced instabilities. In this talk, we detail some approaches on the derivation of cross-diffusion equations from kinetic, fluiddynamical, and stochastic models. Relations to thermodynamic principles and the results of Kawashima and Shizuta are detailed. The entropy structure can also be found in nonstandard applications like van-der-Waals fluids, population dynamics, and exotic financial derivatives. It allows for a mathematical existence theory and stable numerical approximations with guaranteed lower and upper bounds. |
| 講演2： | Linear Boltzmann equation and fractional diffusion |
| Prof. François Golse (Centre de mathématiques Laurent Schwartz, Ecole Polytechnique, France) |
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| 要旨2： | Consider the linear Boltzmann equation of radiative transfer in a half-space, with constant scattering coefficient σ. Assume that, on the boundary of the half-space, the radiation intensity satisfies the Lambert (i.e. diffuse) reflection law with albedo coefficient α. Moreover, assume that there is a tem- perature gradient on the boundary of the half-space, which radiates energy in the half-space according to the Stefan-Boltzmann law. In the asymptotic regime where σ → +∞ and 1 – α ~ C/σ, we prove that the radiation pressure exerted on the boundary of the half-space is governed by a fractional diffusion equation. This result provides an example of fractional diffusion asymptotic limit of a kinetic model which is based on the harmonic extension definition of √-Δ. This fractional diffusion limit therefore differs from most of other such limits for kinetic models reported in the literature, which are based on specific properties of the equilibrium distributions (“heavy tails”) or of the scattering coefficient as in [U. Frisch-H. Frisch: Mon. Not. R. Astr. Not. 181 (1977), 273-280]. |