Center for Mathematical Science and Advanced Technology (MAT)

Seminar Schedule

[MAT Seminar]

Date:

2025/05/14(Wednesday) 13:00-15:00

Language:

English

Location:

MAT Theater, 508, InformationTechnology Building 5F, Yokohama Institute for Earth Sciences (YES)

Speaker:

Takashi Minoshima (MAT)

Title:

Modelling solar energetic particles through spacecraft data assimilation

Abstract:

Solar Energetic Particles (SEPs) are high-energy charged particles ranging from a few keV to several GeV, generated by energetic phenomena on the Sun and subsequently ejected into interplanetary space (Reams 1999). Understanding their origin and dynamics is of great interest to space plasma physics and related fields. Additionally, accurate prediction of the SEP profile is crucial for space weather operations, as SEPs exceeding 10 MeV pose primary threats to the space environment, including radio communication failures, malfunction and degradation of equipment onboard aircraft and satellites, and radiation exposure of astronauts during extravehicular activities. This is expected to grow in importance as human activities expand beyond the Earth’s magnetosphere.
In-situ satellites have been deployed to measure SEPs in the heliosphere, providing information on their acceleration and transport from the Sun. Currently, many satellites are operating to measure SEPs at different radii and longitudes, giving a valuable opportunity to integrate multi-satellite observations with theoretical and numerical studies for comprehensive understanding of SEP physics.
On 30 March 2022, a large solar flare along with subsequent coronal mass ejections led to a SEP event, which was observed simultaneously by the BepiColombo and STEREO-A spacecraft at 0.6 and 1.0 AU, respectively. Fortunately, both spacecraft were positioned approximately along the same interplanetary magnetic field line, giving a good opportunity to investigate SEP transport processes. In this study, we numerically model the SEP intensity profile between 0.6 and 1.0 AU using the focused transport equation along the field line (Ruffolo 1995). By employing the observation data at 0.6 AU as input, the model predicts the SEP profile at 1.0 AU for direct comparison with the observation. To estimate the mean free path, a key transport parameter, we assimilate the observation data at 1.0 AU into the model. The results suggest that the mean free path shortens over time, indicating that scattering gradually affects the SEP transport. This interpretation is qualitatively supported by the independent observation of increasing magnetic field fluctuations at 1.0 AU.

[MAT Seminar]

Date:

2025/05/07(Wednesday) 13:00-15:00

Language:

English

Location:

MAT Theater, 508, InformationTechnology Building 5F, Yokohama Institute for Earth Sciences (YES)

Speaker:

Zhuyuan Lin (MAT)

Title:

Application of coarse-grained molecular dynamics for understanding the rheology, structure, and instability of shallow clay-rich fault

Abstract:

Clay minerals are commonly found on the Earth's surface as products of the chemical weathering of primary minerals. They play a critical role in controlling the rheology and stability of clay-rich faults, including shallow subduction zones. Smectite clay is known for its high water sensitivity and swelling-shrinkage behavior. Shear experiments often characterize smectite clay as frictionally weak but stable, while field observations and clay suspension experiments reveal conditional instability. Despite extensive studies on their frictional properties and fabric development, the underlying mechanisms are not fully unified. Given smectite clay’s ability to carry charge and absorb water, conventional understanding based on friction at the contact surface may not fully explain its shear resistance. A particle-level study on the microscopic shear mechanism can provide deeper insights into the behavior of clay-rich faults. In this seminar, I will introduce the methods and results of shear simulations on a model clay system using molecular dynamics. Clay platelets are simplified as oblate ellipsoids interacting via the Gay-Berne potential. The effects of normal stress and strain rate on the rheology and structure of the model clay system are investigated. Our results suggest that the typical characteristics of clay gouge, including velocity-strengthening behavior and fabric development during shear, can be observed in this simple model clay system. The shear behavior of clay can be described using a yield stress fluid model, beyond conventional considerations of sliding friction. At the end of the presentation, I will briefly explain my main research project at JAMSTEC as a postdoctoral researcher. My research aims to develop new contact models in the discrete element method for weak cohesive materials to fill the scale gap between clay and granular particles. The mixture of strong and weak materials can be applied to study heterogeneous Earth surface materials.

[MAT Seminar]

Date：

2025/3/26(Wednesday) 13:00-15:00

Language:

English

Speaker:

Daniel Shigueo Morikawa

[MAT Seminar]

Date：

2025/3/5(Wednesday) 13:00-15:00

Language:

Japanese

Speaker:

Daisuke Nishiura

[MAT Seminar]

Date：

2025/2/26(Wednesday) 13:00-15:00

Language:

English

Speaker:

Ettore Barbieri

[MAT Seminar]

Date:

2025/02/05(Wednesday) 13:00-15:00

Language:

English

Location:

MAT Theater, 508, InformationTechnology Building 5F, Yokohama Institute for Earth Sciences (YES)

Speaker:

Keisuke Taga (Department of Physics, Waseda University)

Title:

The pattern formation model of the tape-peeling trace by deformed adhesives

Abstract:

It is known that when adhesive tape is peeled, the structure of the peeling front changes depending on the peeling speed, resulting in various patterns on the peeling trace. At slow peeling speeds, a tunnel structure forms as air penetrates the adhesive fluid of the tape, giving it a white appearance. At fast peeling speeds, this tunnel structure collapses, resulting in a black appearance. Particularly at intermediate peeling speeds, these two structures switch chaotically, forming a fractal pattern of spatiotemporal chaos—an intriguing phenomenon in statistical physics and nonlinear systems. Previous studies have proposed models to explain this pattern formation. However, in this study, we proposed other mechanism and formulate a model based on it. In this talk, we will first introduce our proposed model and discuss how fractal patterns emerge within it. We will then compare our model with previous models to highlight its distinctive features and similarities. Finally, we will explore the proposed model from the perspective of scaling properties. Our results suggest that the tape- peeling trace belongs to the directed percolation universality class.

[MAT Seminar]

Date:

2025/1/15(Wednesday) 13:00-15:00

Language:

English

Location:

MAT Theater, 508, InformationTechnology Building 5F, Yokohama Institute for Earth Sciences (YES)

Speaker:

Sota Arakawa (MAT)

Title:

Numerical Investigation on the Compressive Behavior of Hierarchical Granular Piles

Abstract:

Hierarchical granular piles composed of aggregates are key structural features in both geoscience and planetary science, from fault gouge in seismic zones to the internal structures of comets. Although experimental studies have suggested a multi-step evolution in their packing structure, this hypothesis has lacked numerical validation. In this study, we performed large-scale numerical simulations using the discrete element method to investigate the compressive behavior of hierarchical granular piles. We successfully reproduced and confirmed a three-stage evolution process: (i) rearrangement of the aggregate packing structure, (ii) plastic deformation of small aggregates, and (iii) elastic deformation of constituent particles. Additionally, we developed a semi-analytical model for the compression curve, offering insights into the compressive stages and structural dynamics.

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