MASセミナー 2009年度

第20回 MASセミナー

タイトル :Crack Formation Processes in Drying Paste

講演者 : 狐崎 創 氏(奈良女子大学)

日時: 2009年12月16日(水) 16:30 ~ 17:30


アブストラクト: A wide variety of granular materials consolidate by adding a small amount of water, as well known as clay paste and paint. Cracking induced by drying contraction is a typical solid-like behavior of paste, while water can give rheological and porous properties unlike usual solids to granular material sand affect the cracking processes. We review two types of cracking in a uniform layer of drying paste. One is quasi 2-dimensional cracking of paste shrinking on a fixed or frictional boundary. Although resulting cellular structures, named mud crack patterns, have been studied by using an elastic theory, recent studies reveal that such cracking occurs in an earlystage of a drying process and plasticity is significantly important for both creation and growth of cracks. Another type of cracking can be observed in starch pastes in a late-stage of drying process. Cracks are formed gradually from the drying surface and develop into a 3-dimensional prismatic structure. These cracks grow with a propagating drying front, which can be explained by nonlinear water transportation in a porous material. We report analytical and numerical approaches based on spring-network models for these two types of cracking.



第19回 MASセミナー

タイトル :Reaction-diffusion model on tumour growth with contact inhibition

講演者 : 若狭 徹 氏(早稲田大学)

日時: 2009年11月25日(水) 16:30 ~ 17:30


アブストラクト: For the last two decades, the mathematical modeling of tumour growth have been investigated by many researchers. In this talk I will introduce a reaction diffusion model describing spatio-temporal dynamics between two populations of normal cells and abnormal cells, which takes account of the effect of contact inhibition. The purpose of this talk is to understand the qualitative behavior of solutions of our model in one dimensional case. In particular, if the initial supports of two population densities are segregated, then there is a segregated solution in some sense. Moreover, it is observed from the numerical simulations that segregated solutions propagate with constant speed like traveling wave. Then, I will discuss the existence, uniqueness and stability of segregated traveling wave solution of our model.



第18回 MASセミナー

タイトル : Localized Bioconvection of Euglena Caused by Phototaxis in the Lateral Direction

講演者 : 末松 J. 信彦 氏(広島大学)

日時: 2009年11月18日(水) 16:30 ~ 17:30


アブストラクト: A group of micro-organisms often generates a macroscopic ordered pattern such as a bacteria colony and bioconvection. The bioconvection is one of fluidic patterns caused by an upward swimming of the micro-organisms. The oriented swimming is induced in response to an external stimulus or force field, e.g., a gradient in oxygen concentration, light illumination, and gravity. We focused on a swimming micro-organism exhibiting phototaxis, Euglena. In contrast to a general bioconvection appearing all over a chamber, Euglena formed a bioconvection in a part of a chamber. In this seminar, we would like to introduce to the characteristic behavior of bioconvection of Euglena, and discuss the mechanism of the pattern formation based on both experimental results and numerical calculation.



第17回 MASセミナー

タイトル : Phase-field models of liquid-phase epitaxy

講演者 : Prof. Vladimir Chalupecky(九州大学)

日時: 2009年11月11日(水) 16:30 ~ 17:30


アブストラクト: Liquid phase epitaxy is an epitaxial technique for producing thin semiconductor films from liquid supersaturated solutions. In my talk, I will present some mathematical models and their numerical solution that describe the film growth process in the phase-field framework. First, the physical process of crystal growth by liquid phase epitaxy is presented together with various growth morphologies. Single spiral growth is modelled by a phase-field formulation of the Burton-Cabrera- Frank model. Then, we consider a two-scale model that couples the diffusion-convection transport of concentration of atoms in a three-dimensional volume above the epitaxial surface and the microscopic spiral growth at the crystal surface. This model is obtained via a homogenization procedure from the microscopic model. The numerical scheme is based on finite-difference discretization on rectangular cell-centered and stagerred grids. The two-scale nature of the model allows us to use a coarse grid in the three-dimensional volume and a fine grid on the two-dimensional epitaxial surface, thus making the algorithm more efficient. Finally, we also present results of some numerical experiments.



第16回 MASセミナー

タイトル : Numerical and mathematical analyses of water-circulator-induced flow in ponds

講演者 : 中澤 嵩 氏(岡山大学)

日時: 2009年11月04日(水) 16:30 ~ 17:30


アブストラクト: Pollution and muddiness of natural and artificial reservoirs that are used to supply water irrigation have become important problems in recent years. A rotating propeller operating at low speed set on a lake surface is proposed because it is expected that the device can induce vertical circulating flow by the centrifugal force. Although various experiments have shown clearly that the water quality in a lake is improved by operation of such equipment, the flow mechanism is not fully understood. This study is in- tended to characterize vertical circulating flow resulting from the propeller’s action. To survey such a fluid motion numerically and mathematically in simple systems, the flow induced by the top boundary condition which forces a horizontal rotating flow is investigated here. Simulations of flows created by the top boundary condition are carried out to obtain steady-state solutions with various Reynolds numbers and to obtain a transition diagram. �



第15回 MASセミナー

タイトル : New type of evaluation method for level of service criterion using financial theory

講演者 : 大塚 一路 氏(東京大学 先端科学技術研究センター 特任研究員)

日時: 2009年10月14日(水) 16:30 ~ 17:30


アブストラクト: The new type index on the level of service (LOS) criterion is proposed. To identify values of the LOS, we apply the net present value (NPV) method to congestion dynamics formulated by the Logistic equation. We have succeeded in measuring values of infrastructures on the basis of personal available space discounted by waiting time periods.It allows us to rate infrastructures quantitatively including passenger satisfaction. We also compare the theory with the LOS values from raw data observed at immigration counters in an airport. The results statistically reflect intertemporal satisfaction factors that the conventional LOS criterion does not take into consideration.



第14回 MASセミナー

タイトル : Pattern formation in smoldering combustion under micro-gravity

講演者 : 出原 浩史 氏(明治大学 研究推進員)

日時: 2009年10月7日(水) 16:30 ~ 17:30


アブストラクト: It is observed from experiments that the behavior of smoldering combustion under microgravity is completely different from that on the earth. When a piece of paper is burnt in a micro-gravitational environment, interesting ash patterns are observed on the paper. In order to understand how these observed patterns form a model was proposed which has been studied both analytically and numerically. In this talk we will focus on some numerical results, in particular threat from rekindling. As all of the paper is not completely burnt, combustion is sustained by rekindling. We numerically suggest that rekindler occurs from the mathematical model.



第13回 MASセミナー

タイトル : Research for Evacuation and Pedestrian Queueing Systems

講演者 : 柳澤 大地 氏(東京大学大学院、日本学術振興会特別研究員DC1)

日時: 2009年7月29日(水) 16:30 ~ 17:30


アブストラクト: In my talk, I briefly summarize microscopic models for pedestrian dynamics and introduce my two research topics. We have obtained the mathematical formulation for the pedestrian flow, which includes the effect of conflicts and turning. It enables us to verify the specific phenomena for an evacuation theoretically. In the congested evacuation situation, the pedestrian flow decreases when all pedestrians try to evacuate faster and increases when we put an obstacle in front of the exit. When there are plural service windows, the queueing theory indicates that a fork-type queueing system (M/M/s), which collects people into a single queue, is more efficient than a parallel-type queueing system(M/M/ 1×s), i.e., queues for each service windows. However, in our new walking-distance introduced queueing theory, we find that the parallel-type queueing system is more efficient when sufficiently many people are waiting in the queues.



第12回 MASセミナー

タイトル : A hidden edge effect on animal group size and density: an agent-based model revealed

講演者 : 堀内 史朗 氏(明治大学)

日時: 2009年7月22日(水) 16:30 ~ 17:30


アブストラクト: Apart from the foraging conditions and predation pressure, which are often studied concerning the ecological edge effects, we aimed to clarify the boundary nature of edges, from which animals cannot move any farther. By simulating animal groups interacting with one another, we made an agent-based model in a computational space. Assuming no predation pressure, we changed only the resource conditions in contrast between the habitat (comprising ‘interiors’ and ‘edges’) and its ‘exteriors’. The obtained results were robust---only when the resources are sufficiently richer in the habitat than in the exteriors, the group density and size tend to be greater in the interiors than in the edges (i.e. boundaries between the interiors and exteriors); otherwise and more often the group density and size tend to be greater in the edges, or differ little. These were discussed with reference to relevant studies of primates in particular as exemplary group-living animals. We also show that expelling monkeys from edges to interiors---or from farmlands to mountains---work effectively only where the density of monkeys is low, such as Tohoku or Hokuriku areas in Japan Island.



第11回 MASセミナー

タイトル : The stability of a flow on a rotating polar cap

講演者 : 谷口 由紀 氏(明治大学)

日時: 2009年7月15日(水) 16:30 ~ 17:30


アブストラクト: An analytic solution of two-dimensional, steady, linear, viscous flow on a rotating spherical cap is obtained. We calculate a nonlinear solution to the linear solution and observe the stability from the time development of the minute perturbation around the nonlinear flow. As an inflow increases, the nonlinear solution whose configuration differs from that of the linear solution is obtained. The inflow is increases more, the nonlinear solution is unstable by Hopf bifurcation. The position of the occurrence of the instability is first the outlet and second the inlet on the boundary of the spherical cap.


第10回 MASセミナー

タイトル : Micro-Macro Interlocked Simulation of Clouds and Precipitation

講演者 : 島 伸一郎 氏(独立行政法人海洋研究開発機構)

日時: 2009年7月1日(水) 16:30 ~ 17:30


アブストラクト: Although clouds play a crucial role in atmospheric phenomena, the numerical modeling of clouds remains some what primitive. We have proposed a novel, particle based, probabilistic approach for the simulation of cloud microphysics, which is named the Super-Droplet Method (SDM). This method enables accurate simulation of cloud microphysics with less demanding cost in computation. The outline of SDM and our future prospects will be presented. Especially, the possibility to apply Micro-Macro Interlocked simulation framework to the SDM will be discussed.


第9回 MASセミナー

第9回 MASセミナーは延期となりました。ご了承下さい。

タイトル : Traveling wave solutions to a model of some smoldering combustion

講演者 : 出原 浩史 氏(明治大学)

日時: 2009年6月24日(水) 16:30 ~ 17:30


アブストラクト:It is observed from experiments that the behavior of smoldering combustion under microgravity is completely different from that on the earth. When a piece of paper is burnt in a micro-gravitational environment, interesting ash patterns are observed on the paper. In order to understand how these observed patterns form a model was proposed which has been studied both analytically and numerically. In this talk we will focus on some numerical results, in particular the existence of traveling waves. While these traveling waves are relatively simple solutions, they appear to be fundamental to understanding how the ash patterns develop.



第8回 MASセミナー

タイトル : Pattern formation in chemotactic E. coli colonies

講演者 : Thomas Ronald Mollee 氏(明治大学)

日時: 2009年6月17日(水) 16:30 ~ 17:30


アブストラクト: Colonies of E. coli cells form stable two-dimensional spot patterns of surprising regularity when grown on semi-solid agar consisting of a mixture of succinate and amino-acids. The spots, which are dense aggregates of cells, form in the wake of an expanding ring of cells called a swarm ring. Central to this pattern formation process is chemotaxis, the motion of bacteria up gradients of a chemoattractant, which in this case the cells excrete themselves. I will discuss a model of E. coli pattern formation that treats separately the roles played by amino acids and succinate in order to produce the spot patterns and account for the observed migration of the swarm ring.



第7回 MASセミナー

タイトル : Interface evolution by unbalanced tristable Allen-Cahn type equation

講演者 : 大塚 岳 氏 (明治大学)

日時: 2009年5月27日(水) 16:30 ~ 17:30


アブストラクト: Allen-Cahn equation, which is a reaction-diffusion equation expressing phase separation and diffusion, is introduced to express the motion of grain boundaries between two stable phase in a crystal. Formal asymptotic analysis shows that internal layer of the solution approximates the interface motion by mean curvature flow, and the difference of strength of stability between two stable phase derives the driving force to the interface motion. In this talk we introduce a tristable type of Allen-Cahn equation, which expresses the situation including three stable phase and two internal layers. We shall give a brief introduction to the study of singular limit of tristable Allen-Cahn type equation, and discuss the dynamics of internal layer when stabilities of three phase are unbalanced.�



第6回 MASセミナー

タイトル : Fracture Toughness and Maximum Stress in a Disordered Lattice System

講演者 : 占部 千由 氏 (明治大学)

日時: 2009年5月20日(水) 16:30 ~ 17:30


アブストラクト: We will report about fracture in a disordered lattice system. In our system, particles are initially arranged on the triangular lattice and each nearest-neighbor pair is connected with a randomly chosen soft or hard Hookean spring. Every spring has the common threshold of stress at which it is cut. We make an initial crack and expand the system perpendicularly to the crack. We find that the maximum stress in the stress-strain curve is larger than those in the systems with soft or hard springs only (uniform systems). Energy required to advance fracture is also larger in some disordered systems, which indicates that the fracture toughness improves. The increase of the energy is caused by the following two factors. One is that the soft spring is able to hold larger energy than the hard one. The other is that the number of cut springs increases as the fracture surface becomes tortuous in disordered systems.�




第5回 MASセミナー

タイトル : Sexual selection by male choice and human evolution dynamics in complex networks

講演者 : 中橋 渉 氏 (明治大学)

日時: 2009年5月13日(水) 16:30 ~ 17:30


アブストラクト: Sexual selection (Darwin, 1871) is as important as natural selection (Darwin, 1859) for sexual species because we must mate with the other sex to produce progeny. Though Darwin (1871) noticed sexual selection by male choice in the human, theoretical and empirical research on sexual selection has mainly addressed decorative male traits and female preferences for such traits. However, not only in the human but also in many other species, there is increasing evidence of male mate choice for female traits. Why do such male mating preferences evolve and how do they affect the evolution of female traits? In this talk, I will explain quantitative genetic models of sexual selection by male choice to answer these questions and discuss how sexual selection by male choice has affected human evolution.




第4回 MASセミナー

タイトル : Fitness landscapes and the gene regulatory dynamics in complex networks

講演者 : 木下 修一 氏 (明治大学)

日時: 2009年4月22日(水) 16:30 ~ 17:30


アブストラクト : I would like to report two issues: (1) How does the gene network structure influence the fitness landscape in an evolutionary process; (2) How does it influence the dynamics in the gene regulatory network. Long time ago, S. A. Kauffman introduced the so-called "NK-model" that reproduces an evolutionary process of a random network, and he studied fitness landscape under the process, on the one hand. On the other hand, he introduced and studies the famous "Random Boolean network model (RBN)” that describes temporal development of state dynamics of a random network. Both models have been successful to elucidate many important aspects of the random network dynamics. However, recent developments of gene network study have shown that the gene-gene interaction in living cells is not homogeneous like random network but heterogeneous such as scale-free network. Therefore, we need some generalizations of the NK-model and the RBN .So, we have generalized the NK model and the RBN to incorporate the various network structures into the models. Using this generalization, I will discuss the above issues.



第3回 MASセミナー

タイトル : Jamming Formation in Traffic Flow ~ Microscopic and Macroscopic Approach ~

講演者 : 友枝 明保 氏 (明治大学/東京大学)

日時: 2009年4月15日(水) 16:30 ~ 17:30


アブストラクト : Various kinds of jamming phenomena are observed in our daily life. In particular, the dynamics of traffic jam have attracted the interest of researchers in many fields, in terms of a non-equilibrium and dynamical system due to collective motion of interacting particles. In contrast to the continuous (macroscopic) model in the previous talk, our stochastic cellular automaton model (microscopic approach) applicable to buses, trains and other dynamics in conveyance system will be explained in this talk.�



第2回 MASセミナー

タイトル : Jamming Formation in Traffic Flow ~ Microscopic and Macroscopic Approach ~

講演者 : 友枝 明保 氏 (明治大学/東京大学)

日時: 2009年4月08日(水) 16:30 ~ 17:30


アブストラクト :Various kinds of jamming phenomena are observed in our daily life. In particular, the dynamics of traffic jam has attracted the interest of researchers in many fields, in terms of a non-equilibrium and dynamical system due to collective motion of interacting particles. In this study, we have investigated the jamming formation in two new models : one describes the dynamics of one-dimensional traffic flow on a motorway as a compressible fluid model, so-called "macroscopic" approach, and the other describes the dynamics of public conveyance system as a stochastic cellular automaton model, so-called "microscopic" approach. We have shown the unified results that jamming formation is caused by amplifying the small perturbation in both two different approaches. This fact indicates that common structure marvelously underlies the mathematical models for traffic flow.�



第1回 MASセミナー

  • 日時:2009年3月16日13:30〜16:15
  • 場所:明治大学生田校舎・第2校舎A館・A401室
    小田急小田原線 「生田駅」から徒歩10分
    詳しくは, をご覧下さい


  • 13:30~14:15 Alberto Tesei (Rome 1 Univ., Italy)
    Phase transitions, entropy and hysteresis
  • 14:30~15:15 Horst Malchow (Univ. Osnabrueck, Germany)
    Diffusive predation and competition patterns in a noisy environment
  • 15:30~16:15 Kota Ikeda (池田 幸太) (Meiji Univ.)
    Planar traveling Wave in a combustion model




MASセミナーは明治大学グローバルCOEプログラム 『現象数理学の形成と発展』(の援助を受けております。

明治大学先端数理科学インスティテュート・現象数理・基礎数理部門 (世話人:三村昌泰、上山大信、若野友一郎、池田幸太)