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**MIMS現象数理学カフェセミナー
MIMS Cafe Seminar**

世話人：田邊章洋 (Takahiro Tanabe)（明治大学 MIMS研究員）

- 主催： 明治大学先端数理科学インスティテュート(MIMS)
- 会場：明治大学中野キャンパス８階談話室

日時：2019年1月23日(水) 12:40～13:20

Ryo Ito氏 （Meiji University, MIMS）Abstract:

Propagation phenomena appear in various fields of natural science, including population genetics, epidemiology, ecology and so on. The spatially periodic Fisher-KPP equation is among the classical models that describe propagation phenomena. From the viewpoint of ecology, this equation describes the expansion of the territory of invading alien species in a given habitat. The periodic coefficients of the equation represent an environment in which favorable zones and less favorable zones appear alternately in a periodic manner. The aim of this work is to analyze the influence of periodic environment on the invasion speed. In this talk, we discuss the problem of finding optimal periodic coefficient that minimizes the “spreading speed” under certain condition. The term “spreading speed” refers to the asymptotic speed of the propagating front of a solution with compactly supported initial data. From the ecological point of view, the spreading speed describes the invasion speed of alien species. Hence the problem means seeking the best disposition of environment to prevent the invasion of alien species. In order to solve this problem, we introduce a condition under which equality holds in an inequality about the spreading speed derived by Nadin.

日時：2018年12月21日(金) 12:40～13:20

Aya Abe氏 （Meiji University, MIMS）Abstract:

In the origami engineering, some approaches have been done that lead to fundamental and applicational research on the technical aspect for applying Origami to industries. Technology of Origami is used in various ways and development is expected. For example, folding methods that expand and contract large sheets are applied to space structures. Moreover, by folding small structures at the cell level, it is trying to be applied also to the medical field. On the other hand, the honeycomb structure is representative as a light and highly stiff structure and has been widely used as an internal structure of aircrafts or buffer material like cardboard so far. For this honeycomb structure, researches have been done on how to fabricate by folding from a single sheet.

Here, I will introduce two research themes I have worked on so far. One is the result of research on folding and crushing characteristics of pairing origami. The second one is about the research progress and future prospects for the transport box for fruits.

**Instability and pattern formation of the interstellar medium
**

日時：2018年11月19日(月) 12:40～13:20

Ayuki Sekisaka氏 （Meiji University, MIMS）Abstract:

In our universe, there are several types of galaxies. By a shape of their own, they are also called a spiral galaxy, lenticular galaxy, elliptical galaxy and so on. In the study of galaxy formation and evolution, many researchers are interested in the processes that formed a heterogeneous universe from a homogeneous beginning. We also have an interest in the mechanism of pattern formation of the very massive interstellar medium, and unfortunately, the classical physics can not explain the spiral galaxies. One of the model of the self-gravitational interstellar gas clouds is given by the compressible Navier-Stokes-Poisson system (CNSP), and such self-gravitational collapse is called as the Jeans instability.

In this talk, we will show the dynamics of the 3-dimensional CNSP around the Jeans instability point. Second, we want to discuss about the next step of this problem with an audience. This is joint work with Hiroko Yamamoto (University of Tokyo) and Shota Enomoto (Keio University) and supported by MIMS Joint Research Project for Mathematical Sciences.

日時：2018年10月5日(金) 12:40～13:20

Kota Ohno氏 （Meiji University, Graduate School of Advanced Mathematical Sciences）Abstract:

Pattern dynamics has been drawing attention in many research fields. Further, it has been explained using mathematical models. The Belousov–Zhabotinsky (BZ) reaction is a famous experimental model for chemical oscillatory reaction and pattern formation. One can also control the pattern dynamics of the BZ reaction with Ruthenium catalysts by light illumination. Using this property, Vanag et. al. studied global feedback system for the photosensitive BZ reaction and observed anti-phase like oscillations such as standing waves in experimentally. We herein study a simple situation, i.e., diffusive coupled system of two oscillators with global feedback using the photosensitive BZ reaction, to clarify the type of mechanism that causes such anti-phase like behavior both experimentally and theoretically. We observed an in-phase oscillation and two types of anti-phase like oscillations. One is a typical anti-phase oscillation and the other is an alternate oscillation in which each oscillator shows strong and weak peaks alternately. Moreover, we analyzed our model to locate the bifurcational origin and found the reconnection of the bifurcation branches for both anti-phase like oscillations, which was induced by the competition between global feedback and diffusion effect.

*The date was changed to Sep. 19th. *

日時：2018年9月19日(水) 12:40～13:20

Axelle Fleury 氏 （MIMS, Agro Paris Tech)Abstract:

Tropical rainforests cover around 11 million km² of the earth surface and are distinguished by their astounding biodiversity, their essential role in the Earth climate system and the resources they provide to many human populations. The various threats laying upon these valuable ecosystems triggered protection or sustainable exploitation policies and also made even more critical the need to understand their functioning. Being highly complex and diverse environments, part of the research effort consists in designing models which allow to study the key mechanisms and get insight into the possible future of these forests. My work falls within the attempt to answer the following question: will tree species composition of rainforests be affected by the changing climate conditions? The issue has been approached through deterministic modelling, combined with the analysis of a field dataset from a Central African forest. The objective was to look for a model describing a tropical forest tree population, in terms of tree density, and that could account for multiple interactions between tree species groups and between trees and their environment.

**Evolution of symbionts to limit their own cell division for reproductive synchrony with the host
**

日時：2018年7月20日(金) 12:40～13:20

Yu Uchiumi 氏 （Meiji University, MIMS）Abstract:

In mutualism between unicellular hosts and their symbionts, symbiont’s cell division is often synchronized with its host’s. The synchronization ensures the permanent relationship between symbionts and their hosts. However, if symbionts stopped synchronizing their cell division and divided faster than their host, they would proliferate more efficiently. Thus, it seems to be paradoxical that symbionts evolve to limit their own cell division for the synchronization. Here, we theoretically explore the condition for the evolution of self-limited division of symbionts. Our analysis shows that symbionts decrease their cell division rate evolutionarily if not only symbiont’s but also host’s benefit through symbiosis is large. It means that, under mutualistic relationship, symbionts are willing to reduce their cell division rate even if hosts do not force symbionts to limit cell division. Moreover, our result indicates that mutualistic relationship should be established in advance of the evolution of synchronized cell division. This is a joint work with Hisashi Ohtsuki (SOKENDAI) and Akira Sasaki (SOKENDAI).

**Mathematical model of biodiversity arising from competitor-mediated coexistence
**

日時：2018年6月15日(金) 12:40～13:20

Lorenzo Contento 氏 （Meiji University, MIMS）Abstract:

The competitive exclusion principle (CEP), one of the pillars of theoretical ecology, states that when two or more species are competing for the same limited resources only one can eventually survive, the other being driven to extinction. However, in nature many examples of rich biodiversity are observed. Several mechanisms that can lead to species coexistence are known, but most of them occur in situations where the CEP is not applicable. We are interested in studying how indirect competition dynamics can lead to coexistence (competitor-mediated coexistence), without any apparent contradiction with the CEP. The simplest such case is when two otherwise mutually exclusive species are able to coexist thanks to the influence of a competing exotic species. We investigate mathematically this mechanism by a three-species competition-diffusion system, which displays complex patterns of dynamical coexistence even when the exotic invader is “weak”.

**Propagation Phenomena of Bistable Reaction-Diffusion Equations in Spatially Periodic Media
**

日時：2018年5月10日(木) 12:40～13:20

Weiwei Ding 氏 （Meiji University, MIMS）Abstract:

This paper is concerned with the existence and qualitative properties of pulsating fronts for spatially periodic reaction-diffusion equations with bistable nonlinearities. Such an equation arises in modeling a variety of physical and biological phenomena. We focus especially on the influence of the spatial period and, under various assumptions on the reaction terms, we show several existence results when the spatial period is small or large. We also characterize the sign of the front speeds and show the global exponential stability and uniqueness of pulsating fronts with nonzero speed. Furthermore, we give an example where there is no pulsating front with nonzero speed but some non-stationary waves appear. This is a joint work with François Hamel (Aix-Marseille University) and Xiao-Qiang Zhao (Memorial University of Newfoundland).

**Large time behavior of the solutionto the compressible Navier-Stokes equations
**

日時：2018年2月14日(水) 12:40～13:20

Shota Enomoto 氏 （Meiji University, MIMS）Abstract:

In physics, substances are classified into solid, liquid, and gas. Fluids are composed of liquid and gas. We can observe fluids in everyday life, for example, water, oil, alcohol, air and so on. When the stress tensor of a fluid is given by a linear function, that fluid is called a Newtonian fluid. The motion of a Newtonian fluid is governed by the Navier-Stokes equations or Euler equations. In this talk, we introduce a classification for some fluids and we discuss about the stability and asymptotic behavior of some solutions to the compressible Navier-Stokes equations in an infinite layer.

**Modeling of farmers and hunter-gatherers in the Neolithic transition of Europe
**

日時：2018年1月31日(水) 12:40～13:20

Kabir Muhammad Humayun 氏 （Meiji University, MIMS）Abstract:

The Neolithic transition is one of the most significant single developments in human history. Archeological evidence of Neolithic transition suggests that expanding velocity of farmers is roughly constant. To understand such phenomenon, many theoretical attempts have been progressed through mathematical modeling. Existing modeling approaches on Neolithic transition indicates that expanding velocity is faster than the observed one. For understanding of this difference, we propose a three-component reaction-diffusion system which involves two different types of farmers: sedentary and migratory ones. Moreover, we introduce the influence of farming technology on the spread of farmers. Our goal is to study the relation between the expanding velocity and farming technology. In this talk, we focus on the one-dimensional traveling wave solution with minimal velocity and finally our model suggests that the minimal velocity of traveling waves explains the spreading velocity of farmers, which becomes slow down when farming technology is suitably developed. This research is a joint work with Jan Elias (Univ. Graz, Austria), Je-Chiang Tsai (National Tsing Hua Univ., Taiwan) and Masayasu Mimura (Musashino Univ., Japan).

**Variational analysis of Keller-Segel models**

日時：2017年12月5日（火） 12:40～13:20

Yoshifumi Mimura 氏 （Meiji University, MIMS）Abstract:

We introduce the Keller-Segel model for describing the aggregation phenomenon of certain microorganisms called “slime molds”, which have a characteristic property called chemotaxis. Chemotaxis is the motion toward higher concentration of a chemical substance. This kind of microorganism, when put in a nutrition-poor environment, produces a chemical substance that attracts other individuals within the same population. This leads to the formation of an aggregate which produces spores. In this way, the slime molds propagate the next generation. From a mathematical point of view, the aggregation phenomenon can be interpreted as the blow-up of the solution of two simultaneous partial differential equations. In this talk, we show that the blow-up solution never exists if the mass of the slime mold is less than a certain value.

日時：2017年10月26日（木） 12:40～13:20

Yoko Tanokura 氏 （Meiji University, MIMS）Abstract:

With the advent of big data, statistics and data science for modeling data are becoming important. In this seminar, we will briefly explain statistical modeling that describes the fluctuation structure of phenomena based on observation data. Taking examples of familiar phenomena such as consumer prices and stock prices, we will introduce the charm of statistical modeling.

**Extracting Knowledge From Complex Biomedical signals**

日時：2017年7月19日（水） 12:40～13:20

Nina Sviridova 氏 （Meiji University, MIMS）Abstract:

Biomedical signals have been intensively studied over the last decades to meet the need in extensive health monitoring in various areas, from patient's recovery evaluation to maintaining the wellbeing of exercising sportsmen. Although recent equipment and techniques allow one to record numerous biological signals containing rich and promising information regarding the various human body systems performance, still extracting useful information from these signals is a challenging task. In this talk challenges and approaches in analyzing complex biomedical signals will be discussed on the example of human photoplethysmogram. As well photoplethysmogram data recording will be demonstrated.

**Fabricating Multi-View Sculptures**

日時：2017年6月7日（水） 12:40～13:20

Masaki Moriguchi 氏 （Meiji University, MIMS）Abstract:

A multi-view sculpture is an object that appears as drastically different shapes when viewed from different viewpoints. Some of impossible objects, such as "ambiguous cylinders", are special instances of multi-view sculptures, which evoke a sense of impossibility. In this talk, we present a method to compute a multi-view sculpture from in put 2D shapes and viewpoints. To create real physical sculptures, we analyze the topological and geometric properties, and our method considers connectivity, material usage and smoothness of the computed sculpture. Some issues in fabricating sculptures with 3D printers are discussed, and we show preliminary computational results and 3D printed sculptures.

**Multiscale Set-Oriented Computations for Dynamical Systems**

日時：2017年5月10日（水） 12:40～13:20

Tomoyuki Miyaji 氏 （Meiji University, MIMS）Abstract:

Dynamical systems theory provides a useful framework for understanding phenomena in which the state changes dynamically as time passes. In particular, Conley’s fundamental theorem of dynamical systems tells us that any dynamical system can be decomposed into recurrent components and gradient components which connect between the recurrent components. This allows us to describe a dynamical system by a finite directed graph. Although it is difficult to obtain such a decomposition for a concrete example by hand, recent developments of computers and numerical methods have enabled us to obtain it by utilizing a computer. The finite graph description of a dynamical system associated with the Conley indices, which represents the topology and stability of the corresponding recurrent component, is called the Conley-Morsegraph. We briefly introduce a numerical method for computing the Conley-Morse graph for a given dynamical system, and we would like to share some difficulties to overcome.

**A Mathematical Model for Understanding and Creating Impossible Object Illusion**

日時：2017年4月26日（水） 12:40～13:20

Kokichi Sugihara 氏 （Meiji University, MIMS）Abstract:

Impossible objects were first proposed as imaginary 3D structures that exist only in our brains when we see anomalous pictures. It had long been believed that they cannot be realized as actual 3D solids unless we use tricky structures such as discontinuities that appear continuous or curved surfaces that appear planar. However, we found that some of impossible objects can be constructed without those tricks. Starting with this discovery, we have extended the sense of impossibility to various forms. They include “impossible motions”, “ambiguous cylinders”, “partly invisible objects” and “topology-disturbing objects”. We present a mathematical model for understanding pictures of 3D objects, which was first considered for computer vision but also useful for understanding human vision, and show how it can be used for creating new types of impossible objects.

**An Examination for The Iyashi Structure
by Deep Learning**

日時：2016年12月13日（火） 12:10～12:50

Hiroe Abe 氏 （Meiji University, MIMS）Abstract:

Previously for the analysis of Iyashi structure, the mapping function which is obtained from fixtures of facial expressions to the judge by the subject whether the data is healed or not to the subject. This accuracy is determined by the type of inputs and it is not always the general way to select the input data. In recent years, deep learning has been a great concern, because the input data itself is possibly to be provided from the big amounts of data. However, the amount and quality of big data depend on the problem and not yet general-purpose ones are obtained. In this study, the healing structure is given as an example to consider the quality and quantity in the big data.

**Eigenvalue problems from the topological viewpoint**

日時：2016年11月7日（月） 12:10～12:50

Ayuki Sekisaka 氏 （Meiji University, MIMS）Abstract:

Eigenvalue problems are applied in many applications in physics, engineering and in other areas of science. In many cases of mathematics, they are solved by analytical or algebraic approaches. Here, there are other approaches, that is, topological approaches. The topological viewpoint gives simple and beautiful mechanism of mathematics, and is sometimes very convenient in application. In this talk, we roughly explain what is the topological viewpoint of eigenvalue problem with a brief history of topology.

**Recent topics on the phenomenon with respect to camphor**

日時：2016年10月17日（月） 12:10～12:50

Yumihiko S. Ikura 氏 （Meiji University, MIMS）Abstract:

Previously, the self-propelled system driven by the camphor has been understood not only experimentally but also theoretically, e.g., the traffic jam of camphor boats on an annular water channel. In a lot of these studies, to avoid unnecessary complexity, some elements (such as solutal Marangoni convection and fluctuation of water level) were ignored as inconsequential. However, some further suggestions might become impaired. In this café seminar, I would like to introduce some of camphor systems that these elements are thought to be essential for, and claim that this system will include more suggestions.

**A Brief Story of the Lugiato - Lefever Equation**

日時：2016年7月11日（月） 12:10～12:50

Tomoyuki Miyaji 氏 （Meiji University, MIMS）Abstract:

The Lugiato-Lefever equation (LLequation) is a damped driven nonlinear Schrödinger equation with cubicnonlinearity. It was derived by Lugiato and Lefever as a model equation for pattern formation in nonlinear optics in 1987. It exhibits a rich bifurcation structure, e.g. snaking bifurcation of spatially localized structures, breathing localized structure, and spatiotemporal chaos. Nowadays, it is attracting more and more attention in a different context of nonlinear optics. In his caféseminar, we show a brief history of the LL equation as well as a part of our recent interest in this subject.

**Spherical Laguerre Voronoi Diagram as a Tool for Fitting Real World Tessellations**

日時：2016年6月6日（月） 12:10～12:50

Supanut Chaidee 氏 （Meiji University, MIMS）Abstract:

Recently, we proposed a method for fitting real world tessellations, spike-containing objects, using spherical Voronoi diagram and spherical Laguerre Voronoi diagram (SLVD). From the SLVD fitting experiments using ideal data, it leads to the theoretical study of the properties of a polyhedron corresponding to the SLVD. Using those properties, we can solve the SLVD recognition problem, the judgment whether or not the given convex spherical tessellation is SLVD. We finally apply the recognition algorithm to find the best-fitting SLVD to the given spherical tessellation when generators are not included explicitly in the tessellation, which is a generalization of the spike-containing objects. We are now doing the experiments using sugar apple and raspberry photographic images.

This works is supervised by Prof. Kokichi Sugihara.

**Perfect Victory in NHK TV Show “Sugowaza”
from Development of Vehicle Collision Simulation**

**The Lecture date has been changed to May 9th, 2016

※開催日が5月9日に変更になりました変更後の開催日時：2016年5月9日（月） 12:10～12:50

Ichiro Hagiwara 氏（Meiji University, MIMS）Abstract:

Around 1970, for boycotting Japanese cars, astrict safety standard was newly provided in U.S. Since a testcar is around 1 billion yen, to reduce the number of testcars for verifying crash characteristics became the biggest subject concerning the continued existence of vehicle companies over the world. At that time, finite element method(FEM) had been exerting high power in vibration analysis, however had been helpless in collision analysis. I'll talk how to develop the technique for collision simulation using FEM. Also, I’ll tell the road to victory in NHK TV show “Sugowaza(Supreme Skills)” by explaining the relationship between origami engineering and vehicle collision simulation.

**Mathematical Modeling and Analysis of Fruit Skin Patterns**

日時：2015年10月21日（水） 12:10～12:50

Supanut Chaidee 氏 （Meiji University, MIMS）Abstract:

In nature, there are many tessellation patterns on curved surfaces that look like Voronoi diagrams. Typical examples are the patterns found on fruit skins. Verifying that a given tessellation is a Voronoi diagram will be useful for constructing mathematical models of polygonal patterns. However, the data are usually obtained as a 2D projected image, and hence it is not easy to compare it with a Voronoi diagram on a curved surface. We propose frameworks for using a photograph of a fruit to measure the difference between the pattern on its skin and a spherical Voronoi diagram. The problem of finding the spherical Voronoi diagram that best fits the fruit skin pattern is reduced to an optimization problem. In addition, we also find the spherical Laguerre Voronoi diagrams which best fit to the planar tessellations. The validity of this formulation is evaluated using jackfruit and lychee.

**Continuous flattening of polyhedral surfaces**

日時：2015年7月22日（水） 12:10～12:50

Chie Nara 氏 （Meiji University, MIMS）Abstract:

Can we flatten an empty box of paper without cutting and stretching? According to the Cauchy rigidity Theorem (1813) and the Sabitov volume Theorem (1996), it is necessary to change the shape of some faces by moving edges for such motion. Generally, a problem which was proposed by Eric Demaine et al. in 2001 asks to find a continuous flattening motion for any given polyhedron. If the polyhedron is convex, such continuous flattening motion was given with a few methods by the author et al. recently. In this talk, the key ideas are introduced and some future works are proposed.

**A reaction diffusion model for understanding phyllotactic
formation**

日時：2015年6月24日（水） 12:10～12:50

Yoshitaro Tanaka 氏 （Meiji University, MIMS）Abstract:

Phyllotactic patterns in plants are well known to be related to the golden ratio and Fibonacci sequence. Actually, many mathematical models using the theoretical inhibitory effect were proposed to reproduce these phyllotactic patterns. In 1996, Douady and Couder introduced a model using magnetic repulsion and succeeded in reproducing phyllotactic patterns numerically. On the other hand, it was recently revealed in biological experiments that a plant hormone, auxin, regulates the phyllotactic formation as an activator. Then, there arises a natural question as tohow the inhibitory effect can be related to the auxin. In this talk, we will propose a reaction diffusion model by taking account of auxin behavior in plant tips. This model can link the auxin behavior of the activator to the inhibitory effect in the stem tip. Moreover, we will show the relationship between Douady and Couder’s model and our model by singular limit analysis. It also provides us with the potential function corresponding to the inhibitory effect, and the bifurcation diagram.

**Concentration points of solutions in a spatially heterogeneous
reaction-diffusion equation**

日時：2015年5月13日（水） 12:10～12:50

Hiroko Yamamoto 氏 （Meiji University, MIMS）Abstract:

We are interested in a point-condensation phenomenon in solutions of a spatially heterogeneous reaction-diffusion equation. This means that distribution of a solution concentrates in a very narrow region around a finitely many points. Hence, it is important to find the candidates for the concentration points since we can know the shape of concentrating solutions. In this talk, we introduce the location of concentration points and the effect of spatial heterogeneity on the points.

**Development of Origami-forming by modeling and simulation**

日時：2015年3月11日（水） 12:10～12:50

Nguyen Thai Tat Hoan 氏 （Graduate School of Advanced Mathematical Sciences, Meiji University）Abstract:

Origami is a forming process from flat papers to 3D shape by following steps: Shape → Partition → Making crease pattern → Cutting material → Folding → Connecting by glue. In this study, a new manufacturing method called Origami-forming is developed, based on traditional Origami approach. The new method follows the same steps as Origami, applying for wider rank of material (soft and hard material such as aluminum, high tensile steel, etc), and folding by a reconfigurable robot system. If the method is successful, it will allow to produce object in short time and get higher stiffness. In this study, the Origami-forming is applied into Truss Core Panel(TCP) manufacturing, to get the shape that is impossible to be produce by current technology, and acountermeasure to reduce the springback is considered. Secondly, a grooving technique inspired fromtradition origami is proposed to bend the material easier than before, hence allow for a dual-arm robot can produce many cases of shape. A optimization process based on Response surface methodology is built to search for best shape of groove. Next, designing handling system and decision-making process are carried out. Modeling and simulation by FEM is used to confirm forming process.

**Bifurcation Analysis of Periodic Traveling Wave Solutions in Excitable Reaction-Diffusion Systems**

日時：2015年2月18日（水） 12:10～12:50

Mohammad Osman Gani 氏 （Graduate School of Advanced Mathematical Sciences, Meiji University）Abstract:

We are interested in the existence and stability of periodic traveling waves in two-variable excitable reaction-diffusion systems numerically. We introduce a system of reaction-diffusion equations to mimic the cardiac electrical activities. Our results based on the method of continuation show a stability change of Eckhaus type of the periodic traveling waves. There are two families of periodic traveling waves:fast and slow. The fast family is stable in the case of standard FitzHugh-Nagumo excitable system. However, we observe that the fast family becomes unstable in our model. Consequently, it bifurcates to an oscillating wave. We explain this phenomenon by numerically calculating the essential spectra of the periodic traveling waves. Moreover, we study the stability of the periodic traveling waves for the Aliev-Panfilov excitable system and compare its results with the proposed model. This is a joint work with Toshiyuki Ogawa in Meiji University.

**Two-scale expansion with drift approach to
a slow smoldering combustion process in a porous media**

日時：2015年1月28日（水） 12:10～12:50

Ijioma Ekeoma Rowland 氏 （Meiji University, MIMS）Abstract:

We are interested in the upscaling of a slow smoldering combustion process, involving a nonlinear chemical reaction of a solid fuel and an oxidizer on the pore surfaces of a heterogeneous porous media. We introduce the two-scale expansion with drift to derive the upscaled system of equations. Specially, we use this approach to study more general velocity fields arising from dominant convection regime of the flow.

日時：2014年11月5日（水） 12:10～12:50

Tommaso Scotti 氏 （Graduate School of Advanced Mathematical Sciences, Meiji University）Abstract:

Blooms of freshwater cyanobacteria are a worldwide spread environmental issue. In fact, some cyanobacteria can produce a variety of toxins that are harmful to a wide range of organisms, including humans. Therefore, monitoring and understanding the dynamics of harmful algal blooms is tremendously important because of their potential impact on drinking and recreational waters.

Despite toxin producing planktonic species are generally expected to be poor competitors for resources, dense blooms of toxic cyanobacteria, such asMicrocystis, do often occur in nature. We employ a Lotka-Volterra reaction-diffusion system in order to investigate the coupled role of toxicity and zooplankton's predation in the persistence of the toxic species, and to study the mechanisms behind the formation of spatially local toxic blooms. We show that the presence of a toxic prey may destabilize the spatially homogeneous coexistence and trigger the formation of spatial patterns. We also show that local blooms more likely occur when predators avoid the toxic prey and the toxicity is at an intermediate level.

日時：2014年9月24日（水） 12:10～12:50

Kohta Suzuno 氏 （Graduate School of Advanced Mathematical Sciences, Meiji University）

Abstract:

In this talk many types of spontaneous pattern formation in human flow are shown. It is well known that biological entities (fish, birds, ants etc.) behave "as one" and show amazing order without any central controlling unit. Recent development of mathematical science has revealed that the collective motion of pedestrian could also be viewed as a self-organized system. Actually, we can observe self-organized lanes, arches and various structures in simulations and experiments ｏｆ pedestrians, and they are ｎｉｃｅ eｘａmples of the spontaneous order iｎ non-equilibrium finite particle systems. ln this presentation, we review some of the self-organized phenomena observed in crowd simulation and give possible explanations to them via mathematical modeling.

日時：2014年9月10日（水） 12:10～12:50

Takamichi Sushida 氏 （Meiji University, MIMS）

Abstract:

Phyllotaxis is the arrangements of leaves, florets and other organs of plants. In particular, it is well known that typical phyllotactic patterns which appear to plants such as sunflower and pine cone are intimately related to the golden section and Fibonacci sequence. In the classical subject of phyllotaxis, helical models of the cylinder and spiral models of the disk were studied by using the Voronoi diagram and the optimal circle packing, etc. As one of plane tilings, Akio Hizume devised triangular spiral tilings called Fibonacci tornado. Ｔｈｅｙ are tilings which admit a transitive action by a similarity transformation generated by the golden section. Moreover, he presented origami developments of Fibonacci Tornado by one sheet. In this presentation, we will introduce mathematical researches of spiral tilings with phyllotactic properties. In particular, we will consider spiral tilings given as a Voronoi diagram.

日時：2014年8月19日（火） 12:10～12:50

Ryo Ooizumi 氏 （Meiji University, MIMS）

Abstract:

Life history of organisms is exposed to uncertainty generated by internal and external stochasticities. Internal stochasticity is generated by the randomness in each individual life history, such as randomness in food intake, genetic character and size growth rate, whereas external stochasticity is due to the environment. For instance, it is known that the external stochasticity tends to affect population growth rate negatively. It has been shown in a recent theoretical study that internal stochasticity can affect population growth rate positively or negatively. However, internal stochasticity has not been the min subject of researches. Taking account of effect of internal stochasticity on the population growth rate, the fittest organism has the optimal control of life history affected by the stochasticity in the habitat. The study of this control is known as the optimal life schedule problems. ln order to analyze the optimal control under internal stochasticity, we need to make use of "Stochastic Control Theory" in the optimal life schedule problems. There is, however, no such kind of theory unifying optimal life history and internal stochasticity. This study focuses on an extension ｏｆ optimal life schedule problems to unify control theory of internal stochasticity into linear demographic models . We apply our theory to a two-resource utilization model for semelparity. Consequently, we show that the diversity of resources is important for species in a case.

日時：2014年7月16日（水） 12:10～12:50

Yujing Liao 氏 （Meiji University, MIMS）

Abstract:

Computer-based surface models are indispensable in several fields of science and engineering. Reverse engineering is the process of reconstructing digital representations from physical models. Rapid modeling the objects from 2-3 dimensional data is very important task in the scientific research and the market applications. The presented approach is connected to the modeling of 3D objects from the given images. In this talk I will present our technique and related with it applications of the results. (co-researcher: Maria Savchenko)

日時：2013年11月20日（水） 12:10～12:50

Shintaro Kondo 氏 （Meiji University, MIMS）

Abstract:

My research theme is plasma phenomena appearing in nuclear fusion research. When l was a student of the master course of fundamental science and technology at Keio university, I selected it and have researched it. There are many instabilities in plasma phenomena, and drift wave turbulence is a kind of plasma instabilities. In this talk I will speak about plasma phenomena, application, my motivation and the point of my research.

日時：2013年10月23日（水） 12:10～12:50

Yutaka Kobayashi 氏 （Meiji University, MIMS）

Abstract:

One of the most prominent aspects of modern humans' culture, compared with other animals, is said to be its cumulative nature. Namely, humans' culture evolves from generation to generation through accumulation of modifications by individuals. The cumulativeness, however, is not really useful to distinguish modern humans from extinct human species because the latter must also have had cumulative culture. For example, the Levallois flint-knapping technique of Neanderthals for making stone tools is so complex that any single individual could never have invented it alone. One key feature to characterize modern humans' culture then may be its explosive evolution rate. My recent preliminary analysis suggests that explosive culture is possible if knowledge promotes innovation. The presence of a cognitive ability that allows such a feedback however remains to be confirmed. I argue in this talk that "creativity" may be one of cognitive abilities with this property.

Pattern Formation in a Reaction-Diffusion-Advection System

日時：2013年7月3日（水） 12:00～12:50

出原浩史 氏 （明治大学MIMS研究員）

Abstract:

拡散の速さの異なる2種の物質が適当な条件のもとで反応し合うことにより自己組織的に周期的空間構造を作り出すというTuringのパラドックスは、今なお多くの研究を生み出す源となっている。本セミナーでは、Turingのパラドックス、つまり反応拡散系と呼ばれる系に現れる拡散誘導不安定性という一見不可思議な現象を紹介し、それに関連する最近行っているパターン形成に閏する研究についてもお話ししたい。

Modeling Cultural Evolution on Prehistoric Archaeological Data

日時：2013年6月5日（水） 12:00～12:50

青木健一 氏 （明治大学研究・知財戦略機構客員教授）

Abstract:

先史時代とは文字(ましてはマスコミ)以前の時代であり、文化の伝播は人と人の直接の出会いによって主に起きた｡従って、先史時代の文化のダイナミックスは、現代の文化のダイナミックスと異なることが予想される｡本発表では、先史考古学データが物語る2つの現象について、数理モデルを用いた解釈を試みる。 １つ目が、中東からヨーロッパへの初期農耕の地理的伝播である｡Ammerman＆Cavalli-Sforza(1971)によるこの伝播の等速性の発見を受けて、我々(Aoki,Shida,＆Shigesada、l996)は、ヨーロッパに先住する狩猟採集民が進出する農民との接触によって農耕に転向する、反応拡散モデルを提案した｡このモデルから得られる予測は、諸経験的知見と矛盾しない。 ２つ目が、旧人ネアンデルタールと新人サピエンスで異なるとされる文化進化速度である。我々(Aoki,Lehmann,＆Feldman、2011)は、集団遺伝学の分子進化理論を転用して文化進化速度を理論的に定義した｡また、その一応用例として、新人では考古学的に実証されている一対多伝達(一人の熟練者が多くの初心者に教示する)のモデルを提案し先行研究が主張する文化進化の加速効果、文化進化速度に対する集団サイズの影響などについて検討した。

Origami Theory to Design Deployable Structures

日時：2013年5月15日（水） 12:00～12:50

石田祥子 氏 （明治大学特任講師）

Abstract:

折り畳み傘や折り畳み自転車など、“折り畳み”と名のつく製品は私たちの生活になじみ深い。“折り畳む”ことにより持ち運びがしやすく、また省収納スペースを図ることができる。本講演では、曰本古来の文化であり芸術である折紙に着目し、折り畳みが自在な構造物を数学的に設計する手法について論じる。山折線と谷折線を規則的に配置し、軸方向に折り畳み自在な円筒や円錐、中心周りに巻き取ることのできる円形膜などを紹介する。

Propagation Speed of a Starting Wave in a Queue of Pedestrians

日時：2013年5月1日（水） 12:00～12:50

友枝明保 氏 （明治大学MIMS研究員）

Abstract:

渋滞を解消するためには、何を考えれば良いだろうか？ 例えば、高速道路での車の渋滞を考えた場合、渋滞の後方に加わる車の台数を前方から抜けて行く台数よりも少なくすることができれば、渋滞列を短くすることができる。つまり、渋滞にゆっくりと近づき(slow-in)、渋滞から素早く抜け出す(fast-out)ことが実現できれば、渋滞を解消できると言える。本講演では、fast-outに注目し、人が行列から動き出す際の反応の連鎖(発進波)の伝播速度について、その特徴を数理モデルと実証実験の双方から議論する。