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数理科学・先端技術研究分野(MAT)

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 machine-learning-based 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 rock-forming conditions and geological processes that are prevalent in different tectonic settings. Here we present an approach where machine-learning (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.

以降の講演予定
7/24(火)13:00~山本 由弦
7/31(火)13:00〜渡辺 勢也(東京工業大学)
8/21(火)13:00~下林 俊典
※タイトル及び概要は決まり次第掲載いたします

[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 sub-seismic to seismic sliding velocities (mm/s to ms) 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 two-color 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 remote-sensing observations have been devoted to shed light on flare-accelerated 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 X-ray 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 (= gravito-turbulence) or formation of self-gravitating clumps (= fragmentation). Shear stress associated with the gravito-turbulence can transport angular momentum to evolve the radial mass distribution in protoplanetary disks while self-gravitating 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 fore-arc 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 two-phase 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 non-Newtonian 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 limit-cycle 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 3-D 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 3-D models) or perhaps at scales down to meters in vertical 1-D 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 sub-grid scale distributions of plankton biomass are more important to ecosystem dynamics than are the mean-field concentrations represented in typical models. I will briefly present two recent modeling approaches that go beyond grid-based approaches by accounting for: 1) the statistical distribution of mm-scale 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 off-the-grid 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:
Power-law 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 large-scale 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 Tohoku-Oki earthquake, the best observed megathrust earthquake ever in the world, has been explained by viscoelastic models with Newtonian (linear) stress-strain rate relations. All of these linear models were characterized by a thin low-viscosity (weak) layer along the lithosphere-asthenosphere boundary (LAB) in the uppermost mantle. Here we show that a power-law (nonlinear) flow model derived from laboratory experiments incorporating stress-driven afterslip successfully explains the spatially complex pattern of the observation data in 2.8 year after the Tohoku-Oki 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 three-dimensional (3D) heterogeneous structure of the subduction zone, using state-of-the-art techniques in computational science. Our result suggests that LAB has a rapid power-law flow after a subduction zone megathrust earthquake, being temporarily weakened due to large coseismic stress. This is in contrast to the presumption that a low-viscosity 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 low--velocity 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 bio-mimetic-engineering 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.
· Up-to-date 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)micro-structured 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 formation-induced 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 Liquid-Phase Exfoliation of Multilayer 2D Nanomaterials
概要:
Liquid-phase exfoliation is a promising manufacturing method for industrial-scale production of 2D nanomaterials, like graphene, boron nitride and molybdenum disulfide.
Two-dimensional nanomaterials are one-atom-thick layers with extraordinary mechanical, thermal and electronic properties. Their mass production could lead to technological step-changes 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 Mars-sized impactor hit the proto-Earth 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 proto-Earth. However, to date, almost all of the numerical simulations of canonical GIs has concluded that the post-impact disc tends to be impactor-rich. In order to resolve this mismatch, recently, a scenario to form the Moon from the magma ocean on the proto-Earth is suggested. According to the scenario, the majority of heating occurs in the magma ocean on the proto-Earth, which results in the ejection of the target-originated 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 N-body simulations of the accumulation of the Moon carried out on the PEZY-SC 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 one-and-a-half-year oversea dispatch research in EPFL. Turbidity current which flows along the sea or river-floor 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 high-resolution 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 resistance-based 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 lock-gate 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 particle-fluid 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 full-scale three-dimensional 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 super-Earths (ten times the Earth’s mass) to understand the effects of adiabatic compression in the interior of super-Earths. In Miyagoshi et al. (2014, 2015), we showed that the vigor of hot ascending plumes from the core-mantle 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 super-Earths (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 super-Earths 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 shear-thinning 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 out-of-sequence 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 two-dimensional 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 visco-elastoplastic 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 high-density 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 high-density lipoprotein (HDL) particle consists of an open lipid bilayer bound by the alpha-helical apolipoprotein chain apo A-I. Motivated by experimental and numerical studies revealing that discoidal HDL particles exhibit, flat circular, flat elliptical, and saddle-like configurations, a variational description is developed to explore the stability of a flat circular discoidal HDL particle. While the lipid bilayer is modeled as two-dimensional fluid film endowed with surface tension and bending elasticity, the apo A-I is modeled as a one-dimensional inextensible twist-free 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 in-plane elliptical and transverse saddle-like 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 coffee-ring 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 ring-like stain, which is called as 'coffee-ring'. 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 real-scale numerical sandbox experiments
概要:
The stress states in accretionary prisms are important for understanding the building and releasing of seismic energy. The in-situ 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 real-scale and threfore large-scale 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 in-situ 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 micro-scale perturbations. I want to discuss the possibility of the long-term 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 plate-mantle 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 non-dipolar 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 non-uniqueness of heat flux across the core-mantle boundary. Instead of seismic tomographic image or simplified mantle convection model, I impose heat flux across the core-mantle 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 Rayleigh-Benard 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 two-dimensional 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 three-dimensional 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:
Liquefaction-induced 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 liquefaction-induced 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 sand-pebble matrices and the large-sized 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 rip-up-clasts 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 slope-basin 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 lateral-ward. 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.