セミナーのお知らせ
[MATセミナー開催のお知らせ]
 開催日時：
 2018年12月18日(火) 13:00〜15:00
 開催場所:
 横浜研究所 情報技術棟 5階 508 MATシアター
 使用言語:
 英語
 講演者:
 Gen Li （数理科学・先端技術研究分野）
 タイトル:
 On the energetics and stability of a minimal fish school
 概要:
 The behaviors of living beings provide amazing examples of aggregated dynamics that result from complex social reasons. Fish schools are an archetypal example of how local interactions lead to complex global decisions and motions. From the fluid dynamics perspective, hydrodynamic interactions between neighbors in fish schools have often been associated with swimming efficiency strategies, considering how each individual in the school is affected by the vortical flows produced by its neighbors.
The topic of our present study is local hydrodynamic interaction between individuals in small schools of fish, as described in earlier experimental work by Ashraf et al. We therefore study the minimal subsystem of fish school, consisting in two fish swimming together.
The physical basis for fish schooling is examined using threedimensional numerical simulations of a pair of swimming fish, with kinematics and geometry obtained from experimental data. Energy expenditure and efficiency are evaluated using a cost of transport function, while the effect of schooling on the stability of each swimmer is examined by probing the lateral force and the lateral and longitudinal force fluctuations. We construct full maps of the aforementioned quantities as functions of the spatial pattern of the swimming fish pair and show that both energy expenditure and stability can be invoked as possible reasons for the swimming patterns and tailbeat synchronization observed in real fish. Our results suggest that high cost of transport zones should be avoided by the fish. Wake capture may be energetically unfavorable in the absence of kinematic adjustment. We hereby hypothesize that fish may restrain from wake capturing and, instead, adopt sidetoside configuration as a conservative strategy, when the conditions of wake energy harvesting are not satisfied. To maintain a stable school configuration, compromise between propulsive efficiency and stability, as well as between school members, ought to be considered.
Reference
Ashraf, I. et al. Simple phalanx pattern leads to energy saving in cohesive fish schooling. Proceedings of the National Academy of Sciences 114, 9599–9604 (2017).
Ashraf, I., GodoyDiana, R., Halloy, J., Collignon, B. & Thiria, B. Synchronization and collective swimming patterns in fish (Hemigrammus bleheri). Journal of the Royal Society Interface 13 (2016).
[MATセミナー開催のお知らせ]
 開催日時：
 2018年12月4日(火) 14:00〜16:00
 開催場所:
 横浜研究所 情報技術棟 5階 508 MATシアター
 使用言語:
 英語
 講演者:
 田上 大助（九州大学）
 タイトル:
 Mathematical aspects of numerical simulations and its applications to industrial problems
 概要:
 We introduce mathematical foundations of domain decomposition methods for magnetic field problems, and its applications to hugescale computational models. Owing to the unique solvability of mathematical models, we have succeeded at the computations of ultrahugescale computational models of a magnetic field problem, whose numbers of degrees of freedom is about a few billion. We show some numerical examples of applications to practical problems; for example, a thermal therapy device with a precise humanbody model.
Moreover, we introduce some numerical analysis results from the mathematical points of view, which improve accuracy and efficiency of practical numerical computations; for example, some numerical computations of flow problems by using finite element methods and particle methods.
Finally, we also introduce related activities of our institute (Institute of Mathematics for Industry, Kyushu University); for example, researching groundbreaking mathematical technologies, it works to solve mathematical problems that private companies have by joint or commissioned research.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年11月27日(火) 11:00〜12:00
 開催場所:
 横浜研究所 情報技術棟 5階 508 MATシアター
 使用言語:
 英語
 講演者:
 Ettore Barbieri（数理科学・先端技術研究分野）
 タイトル:
 Extreme Deformations of the Elastica for nonconservative forces
 概要:
 The Elastica is a set of nonlinear differential equations describing the deformation of thin filaments. The applications of these equations range from computer vision to DNA modelling. Even though these equations have been studied extensively, little is known of their solution for nonconservative forces.
Examples of nonconservative forces include follower forces, such those forces that always remain perpendicular to the deformed shape.
I will present some closedform solutions of the Elastica under distributed and concentrated loads.
Unprecedented shapes emerge when the magnitude of the force becomes exceedingly large.
I will also analyse the stability of such solutions and the implications from an energetic point of view.
For example, band gaps appear in the strain energy release rates.
Finally, I will discuss the challenges in constructing the experiments aimed at validating the solutions.
This work is in collaboration with Dr Misseroni and Prof Pugno, both at the University of Trento (Italy).
[MATセミナー開催のお知らせ]
 開催日時：
 2018年11月20日(火) 13:00〜15:00
 開催場所:
 横浜研究所 情報技術棟 5階 大会議室
 使用言語:
 日本語
 講演者:
 加藤 恒彦（国立天文台）
 タイトル:
 4次元デジタル宇宙プロジェクトと天文ソフト「Mitaka」について
 概要:
 国立天文台4次元デジタル宇宙(4D2U)プロジェクトは、国立天文台の可視化プロジェクトであり、宇宙・天文学の様々な観測・理論・シミュレーションの研究成果をわかりやすく可視化して一般の人に見せることを主な目的としている。プロジェクトには2本柱があり、１つは天文ソフト「Mitaka」の開発、もう１つはスーパーコンピューターによる数値シミュレーションの計算結果を可視化したムービーの作成である。このうち「Mitaka」の開発については加藤が行っている。
「Mitaka」は様々な観測や理論モデルに基づいて宇宙の様々な天体や構造を見る事ができるソフトであり、地球から出発して、太陽系、恒星の世界、銀河系、銀河団、そして宇宙の大規模構造までの宇宙の階層構造をシームレスに自由に移動して見ることができる。時間を進めて天体の運行や探査機の軌跡などを見ることも可能である。これまで、国立天文台三鷹キャンパスにある立体視ドームシアターで一般向け公開の上映などに使用されてきたほか、Mitaka公式サイト(*1)でフリーソフトとしても公開をしており 、個人での利用、教育用途、上映、展示、講演、テレビ番組、等々、様々な用途で使われてきた。最近ではバーチャルリアリティ（VR）にも対応をしている。
本講演では、4D2Uプロジェクトの概要を説明した後、「Mitaka」について主にお話する予定である。実際にデモンストレーションを行ってどのようなソフトかをご覧いただいた後、Mitakaではどのようなデータやモデルを使い、どのような可視化をしているかについて紹介する。また、Mitakaを用いた立体視上映やVR上映などの事例や開発の経緯などについてもお話ししたい。
(*1) http://4d2u.nao.ac.jp/html/program/mitaka/
[MATセミナー開催のお知らせ]
 開催日時：
 2018年11月6日(火) 13:00〜15:00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 細野 七月
 タイトル:
 The performance model of smoothed particle hydrodynamics with the interactionlistsharing method for manycore architectures
 概要:
 The demands for the optimizing particlebased methods with shortrange interaction forces such as those in smoothed particle hydrodynamics (SPH) is increasing, especially for manycore architectures.
However, because particlebased methods require a large amount of memory access, it is challenging to obtain high efficiency for lowB/F manycore architectures.
Hence, an efficient technique, the socalled “multiwalk” method, was developed in an Nbody gravitational field.
The key of the multiwalk method is in sharing of the interaction lists with multiple particles.
The shared interaction list offers an efficient use of the cache memory in the doubleloops operations for calculating the interactions and reduces the main memory access.
This technique is known to greatly improve the performance of Nbody simulations.
However, such performance improvement is not clear for the problems with shortrange interaction forces such as those in SPH, because the total cost of floating point operations increases when using the shared interaction list.
In this paper, we examine the tradeoff relations between the memory and the cost of floating point operations to optimize the SPH code.
In particular, we predict the wallclock time depending on the number of particles in one group of interaction list for a given device's bandwidth and flops.
To validate our prediction model, we measured the wallclock time spent on a device.
Our model is useful for establishing the efficient choice of the number of particles in one group for the given bandwidth and flops.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年10月30日(火) 13:00〜15:00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 野村 瞬
 タイトル:
 Velocity structure of experimentally produced turbidity current and development of concentration profiling technique by ultrasound backscatter echo signal
 概要:
 Turbidity current flowing with suspended particles is one of the major factors of marine geology. Originally, the real turbidity currents are difficult to observe because no one knows when and where it initiates, but several of them are observed direct or indirect methods. Recent field observations of real turbidity currents are introduced and their damage risks to marine infrastructures are explained.
Then the velocity profiles in experimentally produced turbidity current by continuous suspension supply are discussed. It is found that the unique convex type velocity structure is appeared after passing the unsteady part and it is preserved to the distal area, which would be a key to enhance the sediment transport in long distance.
Additionally, the concentration profiling technique based on ultrasound back scatter echo signal is explained and its applicability to observe inner density profile in turbidity current is discussed by the comparison with image analysis technique.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年10月23日(火) 13:00〜15:00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 西浦 泰介
 タイトル:
 SPH simulation of wave channel Revival edition featuring Davide
 概要:
 The EPFL in Switzerland has studied about tsunami by using a wave channel in laboratory experiment. On the other hand, the MAT has developed the large scale SPH simulation for the tsunami study. However, we need to validate the accuracy and reproducibility of our SPH simulation to apply the numerical model for actual engineering problems. So, there are many good benefits for us to collaborate with each other. As a result of collaboration research, numerical model can be validated by comparing with many experimental data. Furthermore, more complicated phenomena can be simulated by using a numerical model. As a first step, we investigated the wave height and velocity profiles in the case of without buildings. The reproducibility of our SPH simulation was validated and then some points to be improved were pointed out. In this seminar, some results of the collaboration research will be shown towards the investigation of wave impacts on buildings.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年10月16日(火) 13:00〜15:00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 宮腰 剛広 (地球深部ダイナミクス研究分野)
 タイトル:
 About dynamo simulations I want to start, and secondary convection beneath the plate
 概要:
 In the seminar, firstly, I will introduce dynamo simulations which I would like to start although I do not have new results yet. One of the recent interesting discoveries for the Earth’s core is that the thermal conductivity of the fluid metal in the core may be several times larger than the value which was believed in the past. Due to the high conductivity, the age of the inner core is estimated as only several hundred million years. These are important factors to consider the driving source of the geodynamo. From the other viewpoint, we have gotten new findings about convection structure change of liquid metal from experimental studies (collaborating with Dr. Yanagisawa). I would like to talk about dynamo calculations I want to start which are inspired from these new discoveries.
Secondary, I will show numerical simulation results about the secondary convection beneath the moving plate although it is not directly related to the first topic at all. It is known that the heat flow near the ridge is almost proportional to the inverse square root age which is derived from the cooling by the thermal diffusion, but it deviates from the estimation far from the ridge (e.g., Treatise on Geophysics, vol.7, pp.288). For one of the explanations of this deviation, secondary convection beneath the plate (Parsons 1978; Treatise on Geophysics, vol.7, pp.291) is suggested, but it has not been studied in detail in studies of mantle convection simulation. I will show our numerical simulation results of mantle convection in which the secondary convection is formed.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年10月9日(火) 11：00～12：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 古市 幹人
 タイトル:
 Progress of stress chain analysis of largescale DEM simulation of accretionary prism formation
 概要:

Understanding the stress state in accretionary prisms that generate great earthquakes and tsunami, is one of the grand challenges of modern geology. Seamount subduction is generally thought to have strong control on tsunami and earthquake generation. In this contribution, we investigated the stress state associated with a seamount entering the accretionary prisms using realscale numerical sandbox experiments. The simulations are based on the largescale Discrete Element Method (DEM) and use over a billion particles. The simulation of the horizontal shortening of the granular layer with conic indenter shows concaved margins similar to the accretionary prism. The movement of the indenter strongly undulates the thrusts and forms complex lateral stress structures. We assessed the stress state using a stress chain analysis inside the sand layer. Below the initial thickness of the sand layer, the indenter creates a stress field characterized by compaction, while above the initial thickness, strikeslip motion induces compressional stresses oriented along the conjugate frontal thrusts. These two processes cause a rotation of the principal stresses with depth. The technical update from the last study is the use of periodic boundary condition which improves the accuracy of Discrete Fourier Transform (DFT) analysis and naturally handles oblique shorting of the sandbox. Thus, we also show the preliminary result of the sandbox test with oblique shortening condition.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年10月2日(火) 11：00〜12：15
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Davide Wüthrich (EPFL)
 タイトル:
 Extreme Hydrodynamic impact onto buildings
 概要:

Tsunamis, Impulse waves and dambreak waves are rare, but catastrophic phenomena, associated with a large number of casualties and severe damages on infrastructures. However, previous events such as the 2004 Indian Ocean tsunami and the 2011 Tohoku Japan tsunami showed that planning and measures can be implemented to limit human losses and reduce reconstruction costs.
During this seminar, the influence of building geometry on the resulting waveinduced loads is overviewed and discussed. Based on a large experimental program carried out at EPFLLCH in Switzerland, this research generates unsteady flows through a vertical release technique. Initially, the main hydrodynamics properties of both dry bed surges and wet bed bores are identified and characterized in terms of wave profiles, front celerity and velocity profiles. Subsequently, the wave impact against a freestanding building with openings ranging from 0 to 84 % is investigated, measuring forces and moments in all directions. For the impervious configurations, results showed good agreement with the classical hydrodynamic force computed as a function of the momentum flux. The presence of openings induced a flow through the buildings, decreasing the upstream water depths and resulting into a linear reduction of the maximum horizontal force, when compared to the corresponding impervious configuration. The orientation of the building and the presence of debris within the flow also showed to have a key role in the loading process. The final purpose of this study is to provide engineers with practical information for the design of safer vertical shelters in tsunami prone areas.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年9月25日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 蔦谷 匠（生物地球化学研究分野）
 タイトル:
 Modeling the formation of growth layers in human teeth
 概要:

Stable isotope analysis of dentin serial sections of permanent human
tooth has recently proposed as a powerful method to reconstruct
chronological dietary change in infancy and childhood, especially for
breastfeeding and weaning patterns. By sectioning dentin horizontally
in approximately 1 mm thick and analyzing the sections sequentially,
dietary change during the period of tooth formation can be
reconstructed. The number of research that adopts this method
increases. However, human tooth dentin grows like stacked cones, and
the growth lines (i.e, Andersen lines) run obliquely compared to the
sampling planes. Because these lines are cut horizontally in the
existing common method, the derived isotope ratios of individual
sections do not represent accurate dietary change but represent moving
averages. In this study, obliqueness of dentin growth lines, changes
in dentin secretion rate, and dentin outer shape are modeled
mathematically, and its effects on stable isotopic reconstruction of
weaning ages are discussed. The results of this study suggest that
reconstructed weaning ages from the stable isotope ratios of
sequentially sectioned tooth dentin deviate from the true weaning ages
in a certain condition. Better sampling methods or mathematical models
are needed to interpret the stable isotopic results of tooth dentin
serial sections more precisely.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年9月11日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Arthur Bauville（数理科学・先端技術研究分野）
 タイトル:
 Structural styles of accretionary prisms with no preexisting weak layer
 概要:

Decollements constitute the base of accretionary prisms and foldandthrust belts. They allow the occurrence of thinskinned tectonics in which deformation affects only the rocks above the decollement. Often, a preexistent structure serves as decollement, e.g. relatively weak evaporite or shale layers, weakly cemented interlayer planes or layers in with high fluid pressure. However, in other places, there is no evidence for preexisting structures. In this case, the decollement may be seen as a low angle thrust fault. Such fault may be significantly weaker than overlying and underlying rocks because of fracturing, gouge formation, excess fluid pressure or thermal pressurization.
In the absence of a preexisting weak structure, the base of the prism is as strong as the material prism material. In such case, the critical taper theory predicts than one direction of faulting is parallel to the base, i.e. ideally oriented to serve as a decollement. On one hand, sandbox experiments performed in these conditions lead to the stacking of large sediment slices. On the other hand, several authors suggested that this condition must favor tectonic erosion rather than accretion. Furthermore, some natural accretionary prism also doesn’t show evidence of preexisting weak structures.
To reconcile these apparently contradictory natural observations experimental results and theoretical deductions, in this study, we systematically investigate the structural style of accretionary prisms with no preexistent weak layer. We performed numerical simulations based on continuum mechanics to simulate the deformation of sediment. The applied boundary conditions are similar to the ones of a sandbox experiment. We varied the pore fluid factor, cohesion, and plastic weakening coefficient.
The experiment highlights three endmember structural styles. The first one is characterized by underplating with the regular formation of a new frontal thrust. It results in the stacking of large slices of sediment. It is the style characteristics of a sandbox experiment with strong basal friction. The second structural style is characterized by complete underplating with the stacking and exhumation of short slices against the backstop. The last style is characterized by continuous frontal accretion, with a midlevel decollement. In this case, the decollement new frontal thrust is created by splay faulting off the last frontal thrust. The decollement is formed by the connection between successive frontal thrusts.
The transition from one tectonic style to the other is discussed from the viewpoint of the critical taper theory.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年9月4日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 TzuHao Lin（海洋生物多様性研究分野）
 タイトル:
 Machine learningbased soundscape information retrieval and its application in the acoustic remote sensing of marine ecosystems
 概要:

Underwater soundscape, which is a collection of environmental, biological, and anthropogenic sounds, has been considered as an acoustic remote sensing platform of marine ecosystems. By listening to various geophysical events, soniferous animals, and human activities from longduration recordings, it is possible to investigate the temporalspatial variability of marine ecosystems. However, the soundscape analysis remains challenging due to the lack of recognition database and simultaneous source interference.
In recent years, information retrieval techniques based on nonnegative matrix factorization (NMF) have been employed to separate different sound sources with unique spectraltemporal patterns in an unsupervised approach. NMF is a selflearning algorithm which decomposes an input matrix into a spectral feature matrix and a temporal encoding matrix. Therefore, we can stack two or more layers of NMF to learn the spectraltemporal modulation of k sound sources without any learning database. In this presentation, I will introduce the basic concept of NMFbased blind source separation (BSS) and the application in soundscapebased ecosystem monitoring. Finally, I will discuss how to apply the NMFbased BSS to establish an audio recognition database and facilitate the supervised source separation. Now, we are collaborating with Asi@Connect and deploying a toolbox of soundscape information retrieval on the Asian Soundscape. We intend this project as an open science platform, which aims to facilitate the international collaboration on the observation of soundscape dynamics, and wish to collaborate with researchers from marine science, ecological science, and computer science.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年8月28日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 亀山真典（数理科学・先端技術研究分野）
 タイトル:
 Struggle towards numerical modeling of 3D mantle convection with magmatism and plate tectonics
 概要:

We are developing 3D numerical models of mantle convection including the effects of mantle magmatism and plate tectonics, in order to deepen the insights into the thermochemical evolution of the mantles of terrestrial bodies. The mantle magmatism is modeled by the generation of liquid phase (magma) owing to the pressurerelease melting induced by ascending flows of solidstate convection and the motion of the generated magma as a permeable flow through the solid matrix driven by a buoyancy due to the density difference between the solid and the liquid phases. The coherent motion of tectonic plates is, on the other hand, helped by the narrow zones of low viscosity within the highly viscous "lithosphere" along the top cold surface generated by the stresshistorydependent rheology. However, despite their crucial roles in controlling the overall flow structures, these two mechanisms are incompatible with the solidstate convection of the mantle in essence from the numerical aspects: the localized irregularities caused by them severely deteriorate the largescale numerical solution of solidstate convection particularly by the multigrid method. In this presentation, we will show the current status and outcrops of our attempts to overcome the numerical difficulty, together with some examples of 3D experiments running on massive (super)computers.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年8月21日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 下林俊典（数理科学・先端技術研究分野）
 タイトル:
 Phase transitions in intracellular lipid droplets
 概要:

Cholesterol is an essential cell membrane component and the dysregulation of cholesterol levels could lead to lethal diseases,
such as arteriosclerosis. Due to the hydrophobicity, cholesterol is stored in cell membranes or lipid droplets as cholesterol esters (CEs) after the esterification. Interestingly, cholesterol modulates the physical properties of cell membranes and sometimes causes phase transitions, which affects the functions of membrane proteins, such as receptors and transporters. Meanwhile, the occurrence of phase transitions in lipid droplets and biological significance have been still mysterious.
In this seminar, we qualitatively show the intracellular phase transitions in lipid droplets, which are caused by CEs, and discuss the physical principal behind the internal structure using reconstituted artificial lipid droplets and the frank free energy model. Moreover, we would like to show the ongoing work on quantitative investigation of the intracellular phase transitions using Fluorescence Correlation Spectroscopy (FCS).
[MATセミナー開催のお知らせ]
 開催日時：
 2018年7月31日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 日本語
 講演者:
 渡辺勢也（東京工業大学）
 タイトル:
 Multiphase Flow Simulations by Lattice Boltzmann Method with a Blockstructured AMR Method on a GPU System
 概要:

Simulations for multiphase flow require a huge amount of computational resources in order to calculate the phenomenon at the phase interface with high accuracy. We are developing a code of multiphase flow simulations by using the lattice Boltzmann method (LBM) and multiple GPUs. The LBM is suitable for GPU computing and largescale simulations because it is an explicit scheme to solve weakly compressible flows. Direct numerical simulations of gassolid twophase flows such as fluidized bed are realized by coupled the LBM and the discrete element method. By introducing a free surface model into the LBM, we successfully simulated free surface flows interacting with floating objects such as a tsunami.
An adaptive mesh refinement (AMR) method locally assigning highresolution grids is useful for reducing the computation time of multiphase flow simulations. We propose an efficient GPU implementation of the LBM with an octreebased dynamic AMR method. For a simulation in a rectangular domain, highresolution grids are locally assigned based on the forest of octree data structure. For efficient coreless access to a GPU global memory, each leaf has a block of uniform grids. A dynamic load balancing is important in distributed implementations of AMR computations. We propose a new domain partitioning method based on the multiphasefield method for dynamic load balancing of AMR applications.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年7月24日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 山本 由弦（数理科学・先端技術研究分野）
 タイトル:
 Progress of the project for seismicfault drilling on Boso Peninsula
Subductionmegathrust earthquakes in the Japanese metropolitan area
[MATセミナー開催のお知らせ]
 開催日時：
 2018年7月17日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 上木 賢太（地球内部物質循環研究分野）
 タイトル:
 Geochemical Discrimination and feature selection of magmatic tectonic settings using machinelearningbased approach
 概要:

Geochemically discriminating between magmatism in different tectonic settings is a fundamental problem for the geology and geochemistry. It enables us to understand the processes of magma generation within the Earth’s mantle, based on the identification of differences between the rockforming conditions and geological processes that are prevalent in different tectonic settings. Here we present an approach where machinelearning (ML) methods are used for quantitative tectonic discrimination and feature selection using global geochemical datasets containing data for volcanic rocks generated in eight different tectonic settings (Back－arc basin, Continental arc, Continental flood, Island arc, Intra－oceanic arc, Mid－ocean ridge, Oceanic island and Oceanic plateau) with data for 24 elements and 5 isotopic ratios.
This study uses support vector machine, random forest, and sparse multinomial regression (SMR) approaches. All Three ML methods allowed the successful geochemical discrimination between magmas formed in eight different tectonic settings, indicating that magmas formed in different tectonic settings have unique geochemical signatures. It means that magma generation processes are closely connected to the tectonic setting. We found that SMR is a particularly interpretable method because it quantitatively identifies geochemical signatures that characterize the tectonic settings of interest and the characteristics of each sample. These ML methods can also contribute to the identification of the tectonic setting of unknown samples. We will present our methodology, results and its geochemical interpretation.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年7月10日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 桑野 修（数理科学・先端技術研究分野）
 タイトル:
 Thermal imaging method for frictional interface
 概要:

Recent experiments conducted at subseismic to seismic sliding velocities (mm/s to m/s) show the dramatic weakening in the friction coefficient for a wide variety of rock types due to mechanochemical effects by frictional heating. Consequently, several weakening mechanisms have been proposed depending on the type of rock specimens. Some of them are based on the sample observation and analysis after experiments. Direct observation of frictional contacts during an experiment is indisputable to constrain an elementary process at frictional contacts during slip. We developed thermal imaging system for frictional interface applying the principle twocolor thermometry. In this talk, I’ll discuss about accuracy of the present system comparing with conventional infrared thermography.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年7月3日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 簑島 敬（数理科学・先端技術研究分野）
 タイトル:
 Particle acceleration in solar flares: Current understanding and perspective
 概要:

Charged particles in space plasma are sometimes accelerated to relativistic energies by an electromagnetic force. The particle acceleration is a ubiquitous phenomenon in Universe, from Earth to distant astronomical objects such as supernovae and accretion disks around massive stars. The Sun is one of powerful particle accelerators in our space, in which electrons and ions are accelerated more than MeV and GeV energies associated with a flare explosion. Understanding the mechanism of particle acceleration is a long standing issue not only in solar physics but also plasma physics, space physics, and astrophysics. Many remotesensing observations have been devoted to shed light on flareaccelerated particles, and have established that magnetic reconnection plays a fundamental role on the flare and following phenomena. Theoretical and numerical studies have also been conducted to tackle with the particle acceleration mechanism in magnetic reconnection and its associated phenomena (e.g., shock, turbulence, etc.). In this talk, I present current understanding on the flare particle acceleration, and then discuss perspective for a future solar Xray space telescope mission (proposed by NAOJ) that aims to understand the particle acceleration during magnetic reconnection.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年6月26日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 廣瀬 重信（数理科学・先端技術研究分野）
 タイトル:
 Nonlinear outcome of gravitational instability in irradiated protoplanetary disks
 概要:

Gravitational instability (GI) is expected in protoplanetary disks
when they are young and thus massive. The nonlinear outcome of GI is
either fluctuating density waves (= gravitoturbulence) or formation
of selfgravitating clumps (= fragmentation). Shear stress associated
with the gravitoturbulence can transport angular momentum to evolve
the radial mass distribution in protoplanetary disks while
selfgravitating clumps may evolve into companion stars or gas giant
planets. Therefore, understanding the nonlinear outcome of GI is
important for the theory of planet formation. In this talk, I present
3D radiation hydrodynamics simulations to explore the nonlinear outcome
of GI in protoplanetary disks with realistic thermodynamics, where the
realistic thermodynamics is crucial because temperature affects GI very
much. Especially I focus on interpreting the fragmentation condition
obtained from our simulations since the evolution of protoplanetary disks
differs greatly depending on whether fragmentation occurs or not.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年6月19日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 山岸 保子（数理科学・先端技術研究分野）
 タイトル:
 Development of software to predict downtime of future research cruises
 概要:
 Our project aims to provide useful information for planning future research cruises. For this purpose, we constructed a database system for past cruise information of research vessels belonging to JAMSTEC to estimate observation downtime for each cruise. At present, we are developing application to predict the downtime of future research cruise using the data provided by the database system we developed. We firstly statistically analyzed the relationship between the factors, which are season, sea area, vessel, observation equipment, captain, and so on, and the downtime. As a result, we found some problems in developing the application and we have to improve the database system. In this seminar, we will show the problems and the contents of the database refurbishment.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年6月12日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 森重 学（数理科学・先端技術研究分野）
 タイトル:
 Fluid flow inside a thin, low viscosity layer on top of the slab
 概要:
 At least in several subduction zones, thin, low viscosity layers (LVLs) may be needed on top of the slab to explain a low surface heat flow in the forearc region. It is still an open question what controls the formation of LVL, but it is likely that hydrous minerals such as serpentine play essential roles for it. Previous studies have shown that fluid can migrate in the updip direction inside LVL by taking into account permeability anisotropy. In this talk I propose another mechanism for such type of fluid flow based on numerical modeling of twophase flow. I first solve for matrix velocity and dynamic pressure gradient in LVL. Then I solve for fluid flow in and around LVL using the matrix velocity and dynamic pressure gradient obtained in the first step. I find that a large amount of fluid is effectively trapped inside LVL due to the effects of compaction. Also fluid migrates in the updip direction by dynamic pressure gradient. These findings suggest that fluid can migrate along LVL by the combined effects of compaction and dynamic pressure gradient. I also find that fluid tends to stay near the bottom of LVL when nonNewtonian fluid is considered. I will briefly discuss its possible implications for the stability of LVL.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年5月29日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 河村 洋史 （数理科学・先端技術研究分野）
 タイトル:
 Phase reduction approach to synchronization of rhythmic spatiotemporal patterns: From synchronization of beating flagella to metachronal waves of Paramecium
 概要:
 Rhythmic systems and synchronization phenomena are ubiquitous in
nature. Of particular interest is synchronization of rhythmic
spatiotemporal patterns in physical, chemical, and biological systems.
From a mathematical point of view, the oscillatory dynamics can be
considered as limitcycle solutions to partial differential equations.
Recently, we have developed a phase reduction method by which such
partial differential equations can be reduced to an ordinary
differential equation for a single variable called the phase. A key
quantity is the phase sensitivity function, which quantifies the phase
response of a rhythmic system to weak perturbations applied at each
point and at each time. The phase reduction method drastically
facilitates detailed theoretical analysis of the synchronization
dynamics of rhythmic spatiotemporal patterns.
In this talk, we consider the phase reduction approach to
elastohydrodynamic synchronization of beating flagella [Kawamura and
Tsubaki, Phys. Rev. E 97, 022212 (2018)] as a simple example, and
subsequently discuss our mathematical approach to metachronal waves
observed in ciliates such as Paramecium.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年5月15日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Sherwood Lan. Smith （地球環境観測研究開発センター）
 タイトル:
 Can we go Off the Grid? at least for Plankton Ecosystem Modeling
 概要:
 Spatially explicit models, such as the 3D models run on the Earth
Simulator, are typically based on discrete approximations assuming
homogeneity within each grid cell. This means that the concentrations
of nutrients and organisms, and the environmental conditions that
determine their response, are treated as uniform on scales of
kilometers (in 3D models) or perhaps at scales down to meters in
vertical 1D models. Many such models incorporate some representation
of plankton, because they are the sustaining base of marine food webs,
including ultimately fisheries, and also drive important
biogeochemical cycles of nutrients and carbon, which have potentially
important feedbacks with climate. However, plankton range in size from
micrometers to at most centimeters and therefore experience
heterogeneity and intermittency at far smaller scales than such model
grids. Recent observations and modeling studies have revealed that
subgrid scale distributions of plankton biomass are more important to
ecosystem dynamics than are the meanfield concentrations represented
in typical models. I will briefly present two recent modeling
approaches that go beyond gridbased approaches by accounting for: 1)
the statistical distribution of mmscale aggregates of phytoplankton
and associated intermittency in nutrients and zooplankton, and 2) the
active and strategically important motion of plankton that is still
largely ignored in ecosystem models. Each of these approaches gives
results substantially different from typical gridded models. How can
we work together to overcome the remaining challenges and implement
these more realistic offthegrid approaches in spatially explicit
models?
[MATセミナー開催のお知らせ]
 開催日時：
 2018年5月8日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 縣 亮一郎 （地震津波海域観測研究開発センター）
 タイトル:
 Powerlaw flow in asthenosphere weakened by subduction zone megathrust earthquake explains observed surface displacement
 概要:
 The deformation transient that follows large subduction zone
earthquakes is thought to be the response of a largescale interaction
of viscoelastic flow in the asthenospheric mantle and slip on the
megathrust that are accelerated by the sudden coseismic stress change.
The surface measurements of the deformation after the 2011 Mw 9.0
TohokuOki earthquake, the best observed megathrust earthquake ever in
the world, has been explained by viscoelastic models with Newtonian
(linear) stressstrain rate relations. All of these linear models were
characterized by a thin lowviscosity (weak) layer along the
lithosphereasthenosphere boundary (LAB) in the uppermost mantle. Here
we show that a powerlaw (nonlinear) flow model derived from
laboratory experiments incorporating stressdriven afterslip
successfully explains the spatially complex pattern of the observation
data in 2.8 year after the TohokuOki earthquake: Viscoelastic flow
associated with transient spatial variation of effective viscosity is
dominant in overall deformation pattern with opposing horizontal
direction on the seafloor and the land, while afterslip accounts for
eastward displacement on land and offshore outside the rupture area.
These results are obtained using a numerical simulation method
incorporating a fully threedimensional (3D) heterogeneous structure
of the subduction zone, using stateoftheart techniques in
computational science. Our result suggests that LAB has a rapid
powerlaw flow after a subduction zone megathrust earthquake, being
temporarily weakened due to large coseismic stress. This is in
contrast to the presumption that a lowviscosity layer exists at LAB
as a permanent structure because of the presence of water, which has
been justified by a sharp decrease of seismic velocity there. However,
a recent experiment implies that the presence of water does not
account for the existence of a lowvelocity structure, which agrees
to our interpretation.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年4月24日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 堀 宗朗 （数理科学・先端技術研究分野）
 タイトル:
 Problems solved and problems unsolved
 概要:
 In this seminar, I first explain briefly mechanical problems which I have
solved in the last few ten years. This would be a portrait of mine as a
researcher in the field of continuum mechanics. Next, I present a few
problems which I would like to solve in near future. A problem of surface
earthquake fault formation, which is a fracture problem of rock mass, is
explained, focusing on the numerical analysis of slip propagation on a fault
plane. Also, a problem of formulating wave equation in a "principle
coordinate system" is explained; the principle coordinate system is the
coordinate parallel to the principle stress direction for an isotropic
material, and leads to a simpler equation which can be solved more
accurately compared with the wave equation formulated in other coordinate
systems
[MATセミナー開催のお知らせ]
 開催日時：
 2018年4月17日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Gen Li （数理科学・先端技術研究分野）
 タイトル:
 Unveiling Natural Fish Swimming Mysteries and Improving Underwater Vehicle Technology
 概要:
 1. A general introduction to my multidisciplinary area
My research area is the multidisciplinary crossing domain among biology, fluid physics, and engineering. By developing and using advanced computational fluid dynamics approach, my researches explain the mechanism behind natural fish swimming phenomenon, explore the merit in fish body structure and behaviors. Through biomimeticengineering approach, advantages in natural fish swimming can be absorbed to JAMSTEC underwater vehicle technology.
2. My previous/current researches
· An friendly explanation on the concept and merits of on my Computational Fluid Dynamic (CFD) scheme will be provided;
· Several presentative publications will be demonstrated;
· One novel philosophy in fish swimming will be demonstrated: fish swimming behavior is NOT optimized for highest propulsive efficiency (thrust × speed ÷ power), instead, fish adjust their body kinematics to optimize towards minimum transport cost (power ÷ speed）;
· Several other interesting research projects I have participated will also be introduced: 1) Dolphin swim experiment; 2) A boxfish inspired flying robot; 3) Wind turbine blade design, etc.
· Uptodate results of a newly started project on fish schooling.
· Experimental/engineering research project supported by external funding.
3. Future research plan in JAMSTEC
1)schooling swimming–a lot of fish form a school to improve swimming performance;
2)microstructured skin–on fish skin, especially shark, microstructures improve swimming performance
My future plan in JAMSTEC aims to reveal the mechanisms of these two forms of formationinduced hydrodynamic beneficial phenomenon, and provide optimization proposal for Autonomous Underwater Vehicles.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年4月10日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Ettore Barbieri （数理科学・先端技術研究分野）
 タイトル:
 More Than a Peeling  Mathematical Models for LiquidPhase Exfoliation of Multilayer 2D Nanomaterials
 概要:
 Liquidphase exfoliation is a promising manufacturing method for industrialscale production of 2D nanomaterials, like graphene, boron nitride and molybdenum disulfide.
Twodimensional nanomaterials are oneatomthick layers with extraordinary mechanical, thermal and electronic properties. Their mass production could lead to technological stepchanges in electronic devices, solar panels and batteries.
One way to get 2D layers is to peel off a layered material (for example graphite) by mixing it in a liquid solvent and applying a steady shear flow. The shear forces overcome the adhesion forces and separate the layers.
I will present a simple mathematical model relating the critical values of the shear flow with the adhesion of the substrate and the bending stiffness of the layers.
This model gives practical insights on how to minimise the critical shear flow and maximise the peeling.
This work is a collaboration with the research groups of Dr Botto (Queen Mary University of London) and Prof Pugno (Università degli Studi di Trento, Italy).
[MATセミナー開催のお知らせ]
 開催日時：
 2018年3月27日(火) 10：00～12：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 細野 七月 （数理科学・先端技術研究分野）
 タイトル:
 Numerical simulations of the giant impact onto the magma ocean
 概要:
 The Giant Impact (GI) hypothesis is one of the most important phenomena in the planetary science and geoscience as the origin of the Moon.
According to this scenario, a Marssized impactor hit the protoEarth and generate circumterrestrial debris disc, which is later accumulated into the Moon.
Lately, however, the GI has been challenged; the isotope ratios of particular elements show nearly identical values for the bulk component of the Earth and that of the Moon.
This means that the circumterrestrial debris disc should come from the protoEarth.
However, to date, almost all of the numerical simulations of canonical GIs has concluded that the postimpact disc tends to be impactorrich.
In order to resolve this mismatch, recently, a scenario to form the Moon from the magma ocean on the protoEarth is suggested.
According to the scenario, the majority of heating occurs in the magma ocean on the protoEarth, which results in the ejection of the targetoriginated materials.
In order to check whether this scenario is favourable to explain the origin of the Moon, we have carried out a parameter survey of the scenario.
I will show the results of the parameter survey.
I also will show the brief results of the recent Nbody simulations of the accumulation of the Moon carried out on the PEZYSC processors.
[在外研究員等派遣報告会開催のお知らせ]
 開催日時：
 2018年3月23日(金) 15：00～17：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 野村 瞬（数理科学・先端技術研究分野）
 タイトル:
 Experimental investigations on gravity current head and body dynamics
 概要:
 This is the report of oneandahalfyear oversea dispatch research in EPFL. Turbidity current which flows along the sea or riverfloor is important as a formation factor of the subsurface or fluvial topography and a reservoir of petroleum or natural gas for industrial use. In the Bengal fan, it is reported that it travels more than 3800 km and forms gigantic submarine fan. To comprehend the dynamics of turbidity currents, flume experiments are conducted. Using the ultrasound Doppler velocity profiler, the highresolution velocity field in time and space is obtained. After the intrusion of the turbidity current into the ambient water, uplifted flow is observed as head part and relatively steady part is continued as body part. From an electrical resistancebased depositmeter installed in the flume bottom, the sedimentation process is examined, and specific roles of head and body part is discussed. The discrepancies and similarities between particle laden fluid and saline density current are also confirmed using the lockgate type experiment. It is found that turbidity current and saline density current have similar flow structure despite of density differences, while they present somewhat different flow systems induced by the presence or absence of particlefluid interactions.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年3月20日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 西浦 泰介（数理科学・先端技術研究分野）
 タイトル:
 Virtual Laboratory for Geotechnical Centrifuge Tests
 概要:
 In this study, we developed centrifuge model simulations using the discrete element method (DEM) to quantitatively evaluate the earth pressure acting upon box culvert underground structures during the displacement of reverse faults directly beneath the structures. Furthermore, we investigated the reproducibility of ground deformation modes and the earth pressure upon underground structures, through comparison with experimental results. We thus found that the earth pressure on the top slabs of underground structures is constant at the initial earth pressure; although the side wall earth pressure increases with fault displacement. Moreover, we found that the earth pressure acting upon underground structures is affected by the positional relationship between bottom slabs and fault lines. As a result, the fullscale threedimensional DEM simulations proposed in this study offers new possibilities for the physical modelling study of ground deformation scenarios and earth pressure acting upon underground structures in geotechnical centrifuge tests.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年3月13日(火) 10：00～12：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 宮腰 剛広（地球深部ダイナミクス研究分野）
 タイトル:
 Long transition phase of thermal convection with large dissipation number
 概要:
 We have studied thermal convection with large dissipation number which is expected in the interior of massive superEarths (ten times the Earth’s mass) to understand the effects of adiabatic compression in the interior of superEarths. In Miyagoshi et al. (2014, 2015), we showed that the vigor of hot ascending plumes from the coremantle boundary and the efficiency of heat transport by thermal convection are significantly reduced by the effects of adiabatic compression.
In this seminar I will talk about the long initial transient stage of thermal convection with large dissipation number which is expected in massive superEarths (Miyagoshi et al., 2017). When the shallow mantle is initially hotter than the statistical steady state, as expected by giant impacts at the final stage of the formation of large planets, the long transient stage of layered convection is observed. Its duration is about ten billion years and after that it yields to a whole layer convection which is in the statistically steady state. Our results suggest that the thermal convection in many of massive superEarths may be still in the initial transient stage rather than the final steady state
[MATセミナー開催のお知らせ]
 開催日時：
 2018年3月6日(火) 15：00～17：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Georg Stadler (Courant Institute of Mathematical Sciences New York University)
 タイトル:
 Simulation and inference of ice sheet dynamics in Antarctica and Greenland
 概要:
 I will discuss mathematical challenges underlying the modeling, simulation and inference of the dynamics of the Antarctica and Greenland ice sheets. Due to the amount of water stored in these large bodies of land ice, they play a crucial role in predictions of future sea level change. Over long time scales, ice can be modeled as incompressible Stokes fluid with a shearthinning constitutive law. One of the largest uncertainties in the present state of the ice sheets is the boundary condition between the ice and the underlying bedrock. Estimation of these conditions form surface satellite observations is a mathematical inverse problem. This problem is challenging due to its high dimension, in particular if one is interested in quantifying the degree of uncertainty due to the limited surface observations and the imperfect model equations. Such uncertainties translate to uncertainties in predictions of sea level change, and thus have implications for climate policy.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年3月6日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Arthur Bauville （数理科学・先端技術研究分野）
 タイトル:
 Initiation and dynamics of the decollement and outofsequence thrusts in accretionary prisms: a numerical investigation
 概要:
 The dynamics of accretionary prisms has been extensively studied by analytical, analog and numerical models. Generally, the dynamics of the prism is controlled by a relationship between the internal friction of the prism material and the basal friction on the decollement. However, the formation process of the decollement itself remains debated. In some accretionary prisms, such as in the Japan Trench, the presence of a sedimentary layer of lower friction act as decollement layer. In others, such as in the Nankai Trough (Japan), the decollement is a thin zone of high deformation that developed within a thick and seemingly homogeneous sedimentary layer. In this contribution, we investigate the formation of a basal decollement within homogeneous sediments. We use twodimensional numerical simulations with boundary conditions similar to the ones of a sandbox experiment. The imposed boundary conditions are such that a portion of the sediment is dragged outside the box below the backstop. We consider a viscoelastoplastic rheology. Results show that the imposed kinematic boundary conditions, where part of the sediments are dragged outside the box, imply two different orientations of the principal stress direction as well as different elastic loading rates above and below the corner of the backstop. These stress regimes lead to the formation of Andersonian and Riedel faults above and below the backstop corner respectively. The Riedel oriented fault tends to follow the bottom of the box in a fashion similar to a decollement. A lower shear modulus favors larger displacement on individual faults and on the decollement in particular. We propose that this model may explain the formation of decollement within homogeneous sediments such as observed in the Nankai Trough.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年2月28日(水) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 Eliot Fried（沖縄科学技術大学院大学）
 タイトル:
 Shape transitions of discoidal highdensity lipoprotein particles
 概要:
 The packaging and transport of cholesterol in the bloodstream are mediated by nanoparticles called lipoproteins. The functionality of HDL is thought to be closely tied to shape. A discoidal highdensity lipoprotein (HDL) particle consists of an open lipid bilayer bound by the alphahelical apolipoprotein chain apo AI. Motivated by experimental and numerical studies revealing that discoidal HDL particles exhibit, ﬂat circular, ﬂat elliptical, and saddlelike conﬁgurations, a variational description is developed to explore the stability of a ﬂat circular discoidal HDL particle. While the lipid bilayer is modeled as twodimensional ﬂuid ﬁlm endowed with surface tension and bending elasticity, the apo AI is modeled as a onedimensional inextensible twistfree rod endowed with bending elasticity. Stability is investigated using the second variation of the energy functional. Various planar and nonplanar instability modes are obtained and corresponding critical values of the salient dimensionless parameters are determined. The ﬁrst planar and nonplanar unstable modes are tied to inplane elliptical and transverse saddlelike perturbations. With reference to available data, stability diagrams isolate the combinations of input parameters for which a ﬂat circular discoidal HDL particle is linearly stable or unstable.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年2月20日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 下林 俊典 （数理科学・先端技術研究分野）
 タイトル:
 Some new findings on the coffeering effect
 概要:
 If you spill out a drop of coffee on a table and leave it for a while, you may have found a ringlike stain, which is called as 'coffeering'. This phenomenon has become an object of research only twenty years ago, although at least several hundreds of years have passed since human beings started to drink coffee. First, I’ll review what we have learned over the last twenty years in the context of the fundamental mechanism and industrial applications. Second, I’ll present some new findings we have recently discovered. Finally, I’d like to discuss any application possibilities of our findings with you!
[MATセミナー開催のお知らせ]
 開催日時：
 2018年2月13日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 斎藤 貴之（東京工業大学）
 タイトル:
 Variable Inertia Method: an explicit method for mantle convection simulations
[MATセミナー開催のお知らせ]
 開催日時：
 2018年2月6日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 古市 幹人 （数理科学・先端技術研究分野）
 タイトル:
 Orientation of the SHmax in accretionary prisms from realscale numerical sandbox experiments
 概要:
 The stress states in accretionary prisms are important for understanding the building and releasing of seismic energy. The insitu stress states estimated from borehole data in IODP expeditions showed significant deviations in the maximum horizontal stress (SHmax) orientation from the plate convergence. These deviations reflect the 3D structure of the stress state rather than the 2D structure; however the 3D stress structures as well as their effects on the evolution of the accretionary prism are not clear. Analog sandbox experiments can be used to deduce such stress states. We performed realscale and threfore largescale numerical sandbox experiments using the discrete element method to understand the 3D stress state in the accretionary prism. The stress chain analyses demonstrate that the insitu stress orientation from borehole data can be a signal of either the regional direction of plate convergence or the local stress orientation associated with the stress arch. The formation of stress arches is expected by the nonlinearities inherent in crustal deformation and microscale perturbations. I want to discuss the possibility of the longterm monitoring of the SHmax orientations in boreholes to support this hypothesis.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年1月30日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 中川 貴司 （数理科学・先端技術研究分野）
 タイトル:
 Towards understanding geomagnetic secular variations in numerical dynamo simulations with boundary heterogeneities computed from platemantle dynamics model
 概要:
 An aim of this type of simulations is to reveal physics behind geomagnetic secular variations, in particular, formation mechanism of geomagnetic polarity reversals and time evolution of nondipolar components (drifting and standing components). Essentially, those mechanisms have been understood from effects of heterogeneous features of top boundary condition in numerical dynamo simulations but based on seismic tomographic image and very simplified numerical mantle convection model (a series of publications by Olson et al.). However, such a simplified modeling philosophy has avoid addressing with a nonuniqueness of heat flux across the coremantle boundary. Instead of seismic tomographic image or simplified mantle convection model, I impose heat flux across the coremantle boundary computed from numerical mantle convection simulations with more realistic material model and surface plate motions reconstructed from geological data (0 to 200 Ma) in numerical dynamo simulations. in the presentation, I will introduce some of historical backgrounds on numerical dynamo simulations with boundary heterogeneities and current status of this type of research project with showing some of preliminary results.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年1月23日(火) 14：30～16：30
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 柳澤 孝寿（地球深部ダイナミクス研究分野）
 タイトル:
 Flow structures in a liquid metal: formation and destabilization of convection rolls under a horizontal magnetic field
 概要:
 Studies of magnetoconvection and rotating convection by liquid metals are both important for understanding the dynamics of flow in planetary cores. Here we focus on magnetoconvection. We performed laboratory experiments and numerical simulations on the RayleighBenard convection of a liquid metal under an imposed homogeneous horizontal magnetic field.
Flow measurements were performed by Ultrasonic Velocity Profiler that can capture time variations of velocity field even in opaque fluids.
When the intensity of the magnetic field is strong enough, the convection pattern shows almost twodimensional roll structure whose axes are parallel to the magnetic field. Even at that state, we observed nonnegligible velocities of flow in the direction parallel to the magnetic field. Detailed study on the distribution of the flow elucidated that there exists a kind of suction from the side walls to the center. In reducing the intensity of the magnetic field, this component of flow velocity is getting larger and secondary vortices are advected by the flow between the main rolls. On further reduction of the magnetic field, the main rolls begin to fluctuate with large amplitude and threedimensional behaviors become dominant.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年1月16日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 山本 由弦（数理科学・先端技術研究分野）
 タイトル:
 Liquefactioninduced mass transport deposit: structural characteristics and their sequence of intermittent events
 概要:
 Liquefaction of sandy material is quite a common geologic event in plate subduction margins. Once liquefaction occurred, fluid pressure abruptly increase because the architecture of coarse sediments destroyed and pore fluid has to support the overburden pressure. The liquefied sandy sediments lost the shear strength associated with collapse of the architecture, thus liquefaction is major trigger to make submarine mass transport deposits (MTDs).
In this presentation, we are going to present geometry, inner fabric, and their lateral distribution of liquefactioninduced MTDs developed in the late Miocene accretionary prism and the Plio–Pleistocene trench–slope basin sediments in the Miura and Boso Peninsula, central Japan. The MTDs in this area are originally composed of sandpebble matrices and the largesized clasts consisting mudstone or alternating bed of sand and mudstone. The sandy matrix presents no preferred orientation or foliation and commonly intrudes into the large blocks. These occurrences are major difference with the ripupclasts in sandy turbidite deposits, and are indicative of that the liquefied mass, sand/pebble grains with high fluid pressure, behaved like Newtonian fluid. Based on the lateral tracing of a key tephra bed, we identified an evidence of lateral age variation of the MTDs, i.e. younging to the west in the slopebasin deposits. The MTDs may be a result of lateral migration of intermittent submarine slope failures.
A similar systematic pattern can also be identified in sandbox experiments, that slope failures occurred more or less continuously at the same or adjacent locations and sequence of slope failures migrated to the lateralward. The recognition of this failure pattern adds to our understanding of the mechanisms of submarine slope failures and will assist in the prediction of hazardous failures, particularly regarding the occurrence of series of intermittent failures on submarine slopes.
[MATセミナー開催のお知らせ]
 開催日時：
 2018年1月9日(火) 13：00～15：00
 開催場所:
 横浜研究所情報技術棟5階MATシアター
 使用言語:
 英語
 講演者:
 阪口 秀（数理科学・先端技術研究分野）
 タイトル:
 My will for MAT
 概要:
 The department of Mathematical science and Advanced Technology, MAT was established and started in April 2014 under expectation to introduce new trends to JAMSTEC. Since then, MAT members have made great efforts in various research and development topics. Among many results, the work done by Takashi Toyofuku, Miki Y. Matsuo and others (Nature Communications 8, 2017) was one of the most fantastic collaborative output in terms of marriage between mathematical science and biology oriented JAMSTEC research. However, some members of MAT are still struggling only in their own research topics and not able to introduce mathematical sense nor advanced technology for JAMSTEC. In this seminar, I am going to leave my will for MAT and to remind you the function of MAT in JAMSTEC for your future.