Country：Japan

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Country：United States

Country：France

Country：United States

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Country：United Kingdom

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Country：Japan

Country：Japan

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Language：English  

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Other Link： https://arxiv.org/abs/2202.04436

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3389/fphy.2022.1007861

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Other Link： https://www.frontiersin.org/articles/10.3389/fphy.2022.1007861/full

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

We study two-dimensional dense granular flows by molecular dynamics simulations. We quantify shear-induced diffusion of granular particles by the transverse component of particle displacements. In long time scales, the transverse displacements are described as normal diffusion and obey Gaussian distributions, where time correlations of particle velocities entirely vanish. In short time scales, the transverse displacements are strongly non-Gaussian if the system is dense and sheared quasistatically though memory effects on the particle velocities are further suppressed. We also analyze spatio-temporal structures of the transverse displacements by self-intermediate scattering functions and dynamic susceptibilities. We find that the relation between the maximum intensity and characteristic time scale for dynamic heterogeneities is dependent on the models of contact damping (which exhibit different rheological properties such as the Newtonian fluids’ behavior and shear thickening). In addition, the diffusion coefficient over the shear rate is linear (sub-linear) in the maximum of dynamic susceptibility if the damping force is not restricted (restricted) to the normal direction between the particles in contact.

DOI： 10.3389/fphy.2022.992239

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Language：English  

DOI： 10.1063/5.0087578

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsomega.1c04960

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1073/pnas.2118492119

Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1678/rheology.50.63

Other Link： https://www.jstage.jst.go.jp/article/rheology/50/1/50_63/_article/-char/ja

Language：English  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

The mechanical responses of dense packings of soft athermal spheres under a finite-rate shear are studied by means of molecular dynamics simulations. We investigate the volume fraction and shear rate dependence of the fluctuations in the shear stress and the interparticle contact number. In particular, we quantify them by defining the susceptibility as the ratio of the global to local fluctuations. The obtained susceptibilities form ridges on the volume fraction-shear rate plane, which are reminiscent of the Widom lines around the critical point in an equilibrium phase transition.

DOI： 10.3389/fphy.2021.667103

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0sm00856g

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1126/sciadv.aba8766

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.124.225502

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3389/fphy.2020.00099

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We show that non-Brownian suspensions of repulsive spheres below jamming display a slow relaxational dynamics with a characteristic timescale that diverges at jamming. This slow timescale is fully encoded in the structure of the unjammed packing and can be readily measured via the vibrational density of states. We show that the corresponding dynamic critical exponent is the same for randomly generated and sheared packings. Our results show that a wide variety of physical situations, from suspension rheology to algorithmic studies of the jamming transition are controlled by a unique diverging timescale, with a universal critical exponent.

DOI： 10.1103/PhysRevLett.124.058001

DOI： 10.1103/PhysRevLett.124.058001

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C9SM01488H

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5082154

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5086379

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1742-5468/ab3114

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevE.98.012609

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We propose a new method to characterize the spatial distribution of particles' vibrations in solids with much lower computational costs compared to the usual normal mode analysis. We excite the specific vibrational mode in a two dimensional athermal jammed system by giving a small amplitude of active oscillation to each particle's size with an identical driving frequency. The response is then obtained as the real time displacements of the particles. We show remarkable correlations between the real time displacements and the eigen vectors obtained from conventional normal mode analysis. More importantly, from these real time displacements, we can measure the participation ratio and spatial polarization of particles' vibrations. From these measurements, we find three distinct frequency regimes which characterize the spatial distribution and correlation of particles' vibrations in jammed amorphous solids. Furthermore, we can possibly apply this method to a much larger system to examine the low frequency behaviour of amorphous solids with a much higher resolution of the frequency space.

DOI： 10.1039/c6sm00788k

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 8118

Language：English   Publishing type：Research paper (scientific journal)  

Modeling the complex collective behavior is a challenging issue in several material and life sciences. The collective motion has been usually modeled by simple interaction rules and explained by global statistics. However, it remains difficult to bridge the gap between the dynamic properties of the complex interaction and the emerging group-level functions. Here we introduce decomposition methods to directly extract and classify the latent global dynamics of nonlinear dynamical systems in an equation-free manner, even including complex interaction in few data dimensions. We first verified that the basic decomposition method can extract and discriminate the dynamics of a well-known rule-based fish-schooling (or bird-flocking) model. The method extracted different temporal frequency modes with spatial interaction coherence among three distinct emergent motions, whereas these wave properties in multiple spatiotemporal scales showed similar dispersion relations. Second, we extended the basic method to map high-dimensional feature space for application to actual small-dimensional systems complexly changing the interaction rules. Using group sports human data, we classified the dynamics and predicted the group objective achievement. Our methods have a potential for classifying collective motions in various domains which obey in non-trivial dominance law known as active matters.

DOI： 10.1371/journal.pcbi.1006545

PubMed

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

It has recently been revealed that long-wavelength fluctuation exists in two-dimensional (2D) glassy systems, having the same origin as that given by the Mermin-Wagner theorem for 2D crystalline solids. In this paper, we discuss how to characterise quantitatively the long-wavelength fluctuation in a molecular dynamics simulation of a lightly supercooled liquid. We employ the cage-relative mean-square displacement (MSD), defined on relative displacement to its cage, to quantitatively separate the long-wavelength fluctuation from the original MSD. For increasing system size the amplitude of acoustic long wavelength fluctuations not only increases but shifts to later times causing a crossover with structural relaxation of caging particles. We further analyse the dynamic correlation length using the cage-relative quantities. It grows as the structural relaxation becomes slower with decreasing temperature, uncovering an overestimation by the four-point correlation function due to the long-wavelength fluctuation. These findings motivate the usage of cage-relative MSD as a starting point for analysis of 2D glassy dynamics.

DOI： 10.1088/1361-648X/aaa8b8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

By using large-scale molecular dynamics simulations, the dynamics of two-dimensional (2D) supercooled liquids turns out to be dependent on the system size, while the size dependence is not pronounced in three-dimensional (3D) systems. It is demonstrated that the strong system-size effect in 2D amorphous systems originates from the enhanced fluctuations at long wavelengths which are similar to those of 2D crystal phonons. This observation is further supported by the frequency dependence of the vibrational density of states, consisting of the Debye approximation in the low-wave-number limit. However, the system-size effect in the intermediate scattering function becomes negligible when the length scale is larger than the vibrational amplitude. This suggests that the finite-size effect in a 2D system is transient and also that the structural relaxation itself is not fundamentally different from that in a 3D system. In fact, the dynamic correlation lengths estimated from the bond-breakage function, which do not suffer from those enhanced fluctuations, are not size dependent in either 2D or 3D systems.

DOI： 10.1103/PhysRevLett.117.245701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We use computer simulations to analyze the yielding transition during large-amplitude oscillatory shear of a simple model for soft jammed solids. Simultaneous analysis of global mechanical response and particle-scale motion demonstrates that macroscopic yielding, revealed by a smooth crossover in mechanical properties, is accompanied by a sudden change in the particle dynamics, which evolves from nondiffusive motion to irreversible diffusion as the amplitude of the shear is increased. We provide numerical evidence that this sharp change corresponds to a nonequilibrium first-order dynamic phase transition, thus establishing the existence of a well-defined microscopic dynamic signature of the yielding transition in amorphous materials in oscillatory shear.

DOI： 10.1103/PhysRevE.94.022615

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

The violation of the Stokes-Einstein (SE) relation D similar to (h/T)(-1) between the shear viscosity h and the translational diffusion constant D at temperature T is of great importance for characterizing anomalous dynamics of supercooled water. Determining which time scales play key roles in the SE violation remains elusive without the measurement of h. We provide comprehensive simulation results of the dynamic properties involving h and D in the TIP4P/2005 supercooled water. This enabled the thorough identification of the appropriate time scales for the SE relation Dh/T. In particular, it is demonstrated that the temperature dependence of various time scales associated with structural relaxation, hydrogen bond breakage, stress relaxation, and dynamic heterogeneities can be definitely classified into only two classes. That is, we propose the generalized SE relations that exhibit "violation" or "preservation." The classification depends on the examined time scales that are coupled or decoupled with the diffusion. On the basis of the classification, we explain the physical origins of the violation in terms of the increase in the plateau modulus and the nonexponentiality of stress relaxation. This implies that the mechanism of SE violation is attributed to the attained solidity upon supercooling, which is in accord with the growth of non-Gaussianity and spatially heterogeneous dynamics.

DOI： 10.1126/sciadv.1700399

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevlett.123.265501

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.123.265501/fulltext

Language：English  

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Language：English  

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Language：English  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

DOI： 10.1103/PhysRevE.95.069901

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Language：English   Publisher：AMER PHYSICAL SOC  

DOI： 10.1103/PhysRevLett.117.239902

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

DOI： 10.1039/c6sm90096h

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PubMed

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevE.91.012203

Publisher：分子シミュレーション研究会  

DOI： 10.11436/mssj.17.181

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi:10.1209/0295-5075/107/28009

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1103/PhysRevE.89.062315

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1063/1.4873346

Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1063/1.4829442

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Using molecular dynamics simulation on a glass-forming liquid in three dimensions, we investigate the thermal vibrational motions, the configuration changes caused by stringlike jump motions, and their close correlations. The heterogeneous vibrational motions are visualized in terms of a vibration length S-i(t) defined for each particle i. The structure factor for the inhomogeneity of S-i(t)(2) is also calculated, which exhibits considerable long wavelength enhancement. By examining the birth times of strings, they are shown to appear collectively and intermittently. We show that particles with larger S-i(t) tend to trigger jump motions more frequently at later times than those with smaller S-i(t). We also show that the particles with fewer bonds tend to have larger S-i(t) and participate more frequently in the stringlike motions. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770337]

DOI： 10.1063/1.4770337

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1103/PhysRevE.87.012312

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1063/1.4770337

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

To understand the quantitative properties of dynamic heterogeneities on glassy particle systems, we use the theoretical scheme of bond-breakage which can detect configuration rearrangements corresponding to the structural relaxations. It is compared with the four-point correlation scheme for the results of binary mixtures with molecular dynamics simulations of two dimensional NVE ensembles. From the comparisons in the systems, we find superpositions of heterogeneity of configuration rearrangements and that induced by low-frequency vibration modes. The bond breakage scheme detects the long-time relaxations without short-time vibrations. The four-point scheme detects the mixed dynamics of the both. We find that the results on four-point scheme are sensitive to the influence of such vibration modes which gives rise to detectable system-size effects in physical properties. © 2013 American Institute of Physics.

DOI： 10.1063/1.4794679

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The origin of slow dynamics near glass transition and the mechanism of crystal nucleation are two unsolved fundamental problems associated with the metastable supercooled state of a liquid. So far these phenomena have been considered rather independently, however, we have revealed an intimate link between them. Recently we found that crystal-like bond orientational order develops in the supercooled state of (nearly) single-component systems such as spin liquids and weakly polydisperse colloidal liquids. In these liquids, low free-energy configurations in a supercooled liquid have a link to the rotational symmetry which is going to be broken upon crystallization. We argue that this is a direct consequence of that the same free energy governs both glass transition and crystallization at least in this type of liquids. We found that it is such structural ordering at least in this type of liquids that causes glassy slow dynamics and dynamic heterogeneity. Furthermore, we revealed that such structural order also plays a crucial role in crystal nucleation: Crystallization is a process of the enhancement of spatial coherence of crystal-like bond orientational order and 'not' driven by translational order at least in the nucleation stage. These results clearly indicate that the theoretical description at the two-body level is not enough to describe these phenomena and it is crucial to take into account many body correlations, particularly, bond orientational correlations. We argue that there is an intrinsic link between glass transition and crystallization if crystallization does not accompany other processes such as phase separation. If crystallization involves phase separation, on the other hand, such a direct link may be lost. We speculate that even in such a case glassy structural order may still be associated with low free-energy local configurations.

DOI： 10.1063/1.4794561

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1103/PhysRevE.86.041504

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC RHEOLOGY, JAPAN  

We review our recent studies on the structural disorder in crystal, polycrystal, and glass in a Lennard-Jones binary mixture in three dimensions using molecular dynamics simulation. At a low temperature, the crossovers among these states occur as the amount of the large particles is varied. We define a disorder variable D-j (t) for each particle j in terms of local bond order parameters based on spherical harmonics (Steinhardt order parameters). Mesoscopic structural heterogeneity in glass is then visualized. In fcc crystal and polycrystal, we show that stacking faults play an important role in plasticity.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1063/1.3656762

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Spatial confinement is known to induce a drastic change in the viscosity, relaxation times, and flow profile of liquids near the glass (or jamming) transition point. The essential underlying question is how a wall affects the dynamics of densely packed systems. Here we study this fundamental problem, using experiments on a driven granular hard-sphere liquid and numerical simulations of polydisperse and bidisperse colloidal liquids. The nearly hard-core nature of the particle-wall interaction provides an ideal opportunity to study purely geometrical confinement effects. We reveal that the slower dynamics near a wall is induced by wall-induced enhancement of `glassy structural order', which is a manifestation of strong interparticle correlations. By generalizing the structure-dynamics relation for bulk systems, we find a quantitative relation between the structural relaxation time at a certain distance from a wall and the correlation length of glassy structural order there. Our finding suggests that glassy structural ordering may be the origin of the slow glassy dynamics of a supercooled liquid.

DOI： 10.1038/NMAT3034

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi:10.1088/0953-8984/23/19/194121

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi:10.1038/nmat3034

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi: 10.1073/pnas.1001040107

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi:10.1088/0953-8984/22/23/232102

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi:10.1038/nmat2634

Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1103/PhysRevLett.102.185701

Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1103/PhysRevLett.100.099602

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Glasses are formed if crystallization is avoided upon cooling or increasing density. However, the physical factors controlling the ease of vitrification and nature of the glass transition remain elusive. We use numerical simulations of polydisperse hard disks to tackle both of these longstanding questions. Here we systematically control the polydispersity in two-dimensional colloidal simulations, i.e., the strength of frustration effects on crystallization. We demonstrate that medium-range crystalline order grows in size and lifetime with an increase in the colloid volume fraction or a decrease in polydispersity (or, frustration). We find a direct relation between medium-range crystalline ordering and the slow dynamics that characterizes the glass transition. This suggests an intriguing scenario that the strength of frustration controls both the ease of vitrification and nature of the glass transition at least in this system. Vitrification may be a process of hidden crystalline ordering under frustration. This not only provides a physical basis for glass formation, but also an answer to a longstanding question on the structure of amorphous materials: "order in disorder" may be an intrinsic feature of a glassy state of material. Thus our scenario makes a natural connection between structure and dynamics in glass-forming materials, although its relevance should be carefully checked for 3D glass-forming liquids.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://dx.doi.org/10.1103/PhysRevLett.99.215701

Event date： 2023.8

Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

Venue：マキノパークホテル   Country：Japan  

Event date： 2023.8

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：オンライン   Country：Japan  

Event date： 2023.10

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：National Taiwan University, Taipei, Taiwan   Country：Taiwan, Province of China  

Glass transitions are widely observed in various types of soft matter systems. However, the
physical mechanism of these transitions remains elusive despite years of ambitious research.
In particular, an important unanswered question is whether the glass transition is accompanied
by a divergence of the correlation lengths of the characteristic static structures. In this study,
we develop a deep-neural-network-based method that is used to extract the characteristic local
meso-structures solely from instantaneous particle configurations without any information
about the dynamics. We first train a neural network to classify configurations of liquids and
glasses correctly. Then, we obtain the characteristic structures by quantifying the grounds for
the decisions made by the network using Gradient-weighted Class Activation Mapping (Grad-
CAM). We consider two qualitatively different glass-forming binary systems, and through
comparisons with several established structural indicators, we demonstrate that our system
can be used to identify characteristic structures that depend on the details of the systems.
Moreover, the extracted structures are remarkably correlated with dynamics in thermal
fluctuations [1].
Reference:
[1] N. Oyama, S. Koyama, and T. Kawasaki, What Do Deep Neural Networks Find in
Disordered Structures of Glasses?, Frontiers in Physics 10:1007861 (2023).

Event date： 2023.8

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Makuhari Messe,Chiba   Country：Japan  

Event date： 2023.3

Country：Japan  

Language：Japanese  

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Language：Japanese  

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Language：Japanese  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Doshisya University, Kyoto  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：筑波 産総研  

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Language：English  

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Language：English   Presentation type：Oral presentation (invited, special)  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Nagoya  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Fukuoka  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Kyoto  

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Language：Japanese  

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Language：Japanese   Presentation type：Oral presentation (keynote)  

Venue：Nara, Japan  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto, Japan  

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Language：English   Presentation type：Oral presentation (invited, special)  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Nara, Japan  

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Language：English  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Bristol, UK  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (invited, special)  

Country：Malaysia  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：那覇（オンラインハイブリット）   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：名古屋大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：名古屋大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：九州大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：オンライン   Country：Japan  

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Kyoto   Country：Japan  

Audience： College students

Type：University open house

Audience： College students

Type：University open house

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