Language：Japanese   Publishing type：(MISC) Introduction and explanation (bulletin of university, research institution)  

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

Abstract

A series of molecular dynamics simulations were conducted to reveal the fatigue mechanisms in metal nanowires. We applied axial cyclic loading deformation on a copper single-crystal nanowire model and observed the deformation process during cycle evolution. The detailed observation revealed that the deformation mechanisms in the nanowire is essentially different from the case of the macro- and micro-scaled materials because of the lack of dislocation sources. We also found that atomic vacancies were formed continually by dislocation motion even under a simple single-slip condition. The accumulation of vacancies is expected to be a probable mechanism of fatigue in nanomaterials.

DOI： 10.1088/1361-651x/acea3b

Other Link： https://iopscience.iop.org/article/10.1088/1361-651X/acea3b/pdf

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

Authorship：Last author   Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

DOI： 10.18999/njhpfs.46.1.23

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.38.011176

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

Spontaneous pattern formation by a large number of dislocations is commonly observed during the initial stages of metal fatigue under cyclic straining. It was experimentally found that the geometry of the dislocation pattern undergoes a crossover from a 2D spot-scattered pattern to a 1D ladder-shaped pattern as the amplitude of external shear strain increases. However, the physical mechanism that causes the crossover between different dislocation patterns remains unclear. In this study, we theorized a bifurcation diagram that explains the crossover between the two dislocation patterns. The proposed theory is based on a weakly nonlinear stability analysis that considers the mutual interaction of dislocations as a nonlinearity. It was found that the selection rule among the two dislocation patterns, “spotted” and “ladder-shaped”, can be described by inequalities with respect to nonlinearity parameters contained in the governing equations.

DOI： 10.3390/sym15051028

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Part of collection (book)   Publisher：Springer Nature Singapore  

DOI： 10.1007/978-981-99-0015-2_1

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The reaction–diffusion equation approach, which solves differential equations of the development of density distributions of mobile and immobile dislocations under mutual interactions, is a method widely used to model the dislocation structure formation. A challenge in the approach is the difficulty in the determination of appropriate parameters in the governing equations because deductive (bottom-up) determination for such a phenomenological model is problematic. To circumvent this problem, we propose an inductive approach utilizing the machine-learning method to search a parameter set that produces simulation results consistent with experiments. Using a thin film model, we performed numerical simulations based on the reaction–diffusion equations for various sets of input parameters to obtain dislocation patterns. The resulting patterns are represented by the following two parameters; the number of dislocation walls (p2), and the average width of the walls (p3). Then, we constructed an artificial neural network (ANN) model to map between the input parameters and the output dislocation patterns. The constructed ANN model was found to be able to predict dislocation patterns; i.e., average errors in p2 and p3 for test data having 10% deviation from the training data were within 7% of the average magnitude of p2 and p3. The proposed scheme enables us to find appropriate constitutive laws that lead to reasonable simulation results, once realistic observations of the phenomenon in question are provided. This approach provides a new scheme to bridge models for different length scales in the hierarchical multiscale simulation framework.

DOI： 10.3390/ma16052108

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

DOI： 10.7566/JPSHT.3.002

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/JPSJ.91.104801

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

In general, the insertion of Stone-Wales (SW) defects into single-walled carbon nanotubes (SWNTs) reduces the buckling resistance of SWNTs under axial compression. The magnitude of reduction is more noticeable in zigzag-type SWNTs than armchair- or chiral-type SWNTs; however, the relation between the magnitude of reduction and aspect ratio of the zigzag SWNTs remains unclear. This study conducted molecular dynamics (MD) simulation to unveil the buckling performance of zigzag SWNTs exhibiting SW defects with various tube diameter. The dependencies of energetically favorable buckling modes and the SW-defect induced reduction in the critical buckling point on the tube diameter were investigated in a systematic manner. In particular, an approximate expression for the critical buckling force as a function of the tube diameter was formulated based on the MD simulation data.

DOI： 10.3390/nano12152617

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

DOI： 10.1038/s41598-022-16703-4

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

DOI： 10.3390/ma15144929

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

Explicit and tractable formulation of the internal stress field around edge dislocations is indispensable for considering the mechanics of fine crystalline solids, because the motion of edge dislocations in a slanted direction with respect to the free surface often plays a vital role in the plastic deformation of the solids under loading. In this study, we formulated an analytical solution for the stress distribution that occurs around edge dislocations embedded in a semi-infinite elastic medium. This formulation is based on the image force method and the Airy stress function method; it describes the variation in the stress distribution with changes in the slanted angle between the traction-free flat surface of the medium and the Burgers vector of the edge dislocation. Furthermore, our analytical solution shows that the attractive force acting on the edge dislocation due to the presence of the free surface is always perpendicular to the surface, regardless of the relative angle of the Burgers vector with the surface.

DOI： 10.1098/rsos.220151

Other Link： https://royalsocietypublishing.org/doi/full-xml/10.1098/rsos.220151

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

The form-factor for the stem surface area is directly proportional to the square root of the form-factor for the stem volume, i.e., the square root law of the form-factor. Although the square root law addresses the stems of coniferous trees, the nature of the proportional coefficient of the law has not been discussed. In this study, we demonstrated that the coefficient indicates the stem taper; therefore, it is named "Taper Index based on Form-Factor (TIFF)." We also examined the relationship between the form-factor for the culm surface area and the form-factor for the apparent culm volume of 570 culms across three bamboo species (Phyllostachys pubescens Mazel ex Houz., P. bambusoides Sieb. et Zucc., and P. nigra var. henonis). The square root law held true for all three bamboo species. The species-specific TIFF was determined to be 0.873 for P. pubescens, 0.897 for P. bambusoides, and 0.901 for P. nigra. This result implied that P. pubescens had a more tapering culm form compared to the other two species, while culm taper was similar between P. bambusoides and P. nigra. Our findings align with empirical observations of the culm taper of the bamboo species. Intra-species variation in TIFF was considerably small, allowing us to evaluate the species-specific culm taper from a small number of samples. Therefore, we conclude that TIFF provides a simple and useful method for quantifying species-specific culm or stem taper, and facilitates the estimation of merchantable or total volume.

DOI： 10.1007/s10342-021-01416-6

Web of Science

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

DOI： 10.1103/PhysRevE.104.025009

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

DOI： 10.1029/2020EA001457

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

DOI： 10.1017/qpb.2020.5

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

DOI： 10.3390/app10207163

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Royal Society  

Road corrugation refers to the formation of periodic, transverse ripples on unpaved road surfaces. It forms spontaneously on an initially flat surface under heavy traffic and can be considered to be a type of unstable growth phenomenon, possibly caused by the local volume contraction of the underlying soil due to a moving vehicle’s weight. In the present work, we demonstrate a possible mechanism for road corrugation using experimental data of soil consolidation and numerical simulations. The results indicate that the vertical oscillation of moving vehicles, which is excited by the initial irregularities of the surface, plays a key role in the development of corrugation.

DOI： 10.1098/rspa.2020.0323

Other Link： https://royalsocietypublishing.org/doi/full-xml/10.1098/rspa.2020.0323

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.eml.2020.100970

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

Hollow-section columns are one of the mechanically superior structures with high buckling resistance and high bending stiffness. The mechanical properties of the column are strongly influenced by the cross-sectional shape. Therefore, when evaluating the stability of a column against external forces, it is necessary to reproduce the cross-sectional shape accurately. In this study, we propose a mathematical method to describe a polygonal section with rounded edges and vertices. This mathematical model would be quite useful for analyzing the mechanical properties of plants and designing plant-mimicking functional structures, since the cross-sections of the actual plant culms and stems often show rounded polygons.

DOI： 10.3390/sym12060996

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Taylor & Francis Group  

DOI： 10.1080/13416979.2019.1690723

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

DOI： 10.1103/PhysRevB.100.155116

Web of Science

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.7566/JPSJ.88.024001

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

DOI： 10.1016/j.physe.2018.08.006

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Woodhead Publishing  

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

DOI： 10.12989/csm.2018.7.5.611

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

DOI： 10.1007/s11676-018-0767-6

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

To reveal the atomistic scale mechanism of buckling of single-walled carbon nanotubes (SWCNTs) under axial compression, we carried out molecular dynamics (MD) simulation and atomistic structural instability (ASI) analysis. The ASI analysis enables us to reveal the development of ‘latent’ instability modes until buckling of structure, which cannot be clarified with MD alone. Euler-type buckling was found in relatively thin and long nanotube models, while buckling triggered by change of cross-sectional shape (i.e., radial buckling) was found in thick and short models. With growing radius, a crossover between the Euler-type and radial buckling modes was clearly found in the ASI analysis. Even when the deformation behavior was apparently the same, the buckling can be triggered by different instability modes. We also analyzed the structural instability using the Flügge theory based on linear continuum mechanics (LCM) to compare the results with the ASI analysis. Initial eigenvalues and development of instability modes were different between the ASI and LCM results, leading to a significant deviation of buckling strain and instability crossover points. We investigated the effect of chirality of CNT which is difficult to explain by LCM.

DOI： 10.1016/j.physe.2018.05.035

Scopus

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

Bamboo forests are likely to be subjected to self-thinning due to their rapid growth rate. In fully stocked bamboo forests, the stand density (ρ) was suggested to be inversely proportional to the square of mean diameter at breast height (D) (ρ ∝ D−2), differing from the conventional power-law for trees, i.e., Reineke equation (ρ ∝ D−1.6). Nevertheless, the validity and mechanism of the inverse-square law remained unclear, despite its significance for managing bamboo forests. In this study, we derived an allometric model that predicts the slope of the maximum size-density relationship (MSDR) between D and ρ on double logarithmic coordinates based on well-known ecological laws. The model indicates that the slope of −2 for bamboo is theoretically valid, with the difference in the slope between bamboo and trees being caused by their differences in inner-culm (or inner-stem) structure. We also determined the MSDR empirically by compiling data of 415 Phyllostachys pubescens Mazel ex Houz. pure stands across Japan. The obtained MSDR describes the upper boundary of the D-ρ relationship well, with a slope of −1.996 that is very close to − 2. We further established a stand density management diagram of P. pubescens stands based on the MSDR. This diagram allows forest managers to regulate ρ depending on D as well as management purposes (production of bamboo shoot, bamboo charcoal and culm wood).

DOI： 10.1016/j.foreco.2018.05.044

Scopus

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

It is strongly debated whether bamboo forest ecosystems are a carbon sink or a carbon source because of insufficient knowledge regarding carbon loss via CO2 emissions from these forests. The surface area (S) of bamboo culms (stems) is important for estimating culm respiration, a major component of carbon cycling in bamboo forests. However, few studies have attempted to formulate predictive equations for S. In this study, we developed allometric equations for predicting S in three bamboo species grown in Kyushu Island, western Japan: Phyllostachys pubescens Mazel ex Houz., P. bambusoides Sieb. et Zucc. and P. nigra var. henonis. We used a power equation between S and diameter at breast height (D) and a linear equation between S and D × total culm length (H). The results indicated that P. bambusoides and P. nigra shared common site-independent equations. In contrast, P. pubescens required species-specific equations due to interspecific variation in culm slenderness and tapering. We also found that D was a better predictive variable than DH when quantifying S because of its satisfactory predictive performance and simplicity. These findings will be beneficial for evaluating the contribution of bamboo forest ecosystems to carbon cycling.

DOI： 10.3390/f9060295

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media S.A.  

DOI： 10.3389/frym.2018.00005

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society for Science on Form  

DOI： 10.5047/forma.2018.001

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejam.74.51

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

Team coordination is a basic human behavioral trait observed in many real-life communities. To promote teamwork, it is important to cultivate social skills that elicit team coordination. In the present work, we consider which social skills are indispensable for individuals performing a ball possession game in soccer. We develop a simple social force model that describes the synchronized motion of offensive players. Comparing the simulation results with experimental observations, we uncovered that the cooperative social force, a measure of perception skill, has the most important role in reproducing the harmonized collective motion of experienced players in the task. We further developed an experimental tool that facilitates real players' perceptions of interpersonal distance, revealing that the tool improves novice players' motions as if the cooperative social force were imposed.

DOI： 10.1103/PhysRevE.97.022410

Scopus

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Institute of Physics  

Carbon nanocoil (CNC) is a carbon nanofiber with helical shape. In this study, we fabricated CNC-based composites endowed with electromagnetic wave absorption property. CNCs were synthesized by chemical vapor deposition using acetylene as a precursor and Fe and SnO2 particles as catalysts. The composites were produced by dispersing CNCs into epoxy resin or paraffin by ultrasonication, and then hardening a droplet of the solution on an aluminum substrate with ca. 2mm in specimen thickness. Paraffin was used as a solvent when producing the composites with the CNC concentration higher than or equal to 5wt.%
otherwise epoxy was used. The reflection ratio of the composites with different concentrations were measured by the free space method using lens antennas in frequency ranges of 5.6-40 and 67-110 GHz. The CNCs/epoxy composites of 0.1-1.0 wt.% showed poor reflection losses. The 10 wt.% CNCs/paraffin composite achieved a reflection loss of -32 dB at 79.2 GHz. Its bandwidth corresponding to the reflection loss below -20 dB was 4.85 GHz. The CNCs/paraffin composite also turned out to show a good absorption property in W band frequencies (75- 110 GHz).

DOI： 10.1063/1.5021934

Scopus

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

Granular surfaces subjected to repeated passage often spontaneously develop a corrugated pattern. In this study, we scrutinized the growth dynamics of surface corrugation in a self-rotating sand bed that is traced by the edge of a vertically oscillating arm. We found that both the rotation velocity and the frequency of the oscillator strongly affect the occurrence rate of corrugation as well as the time evolution in the corrugation pattern, due to the intermittent collision between the oscillator and sand bed. We also discovered that the growth dynamics involves two distinct collective modes that describe the translational motion of the corrugation pattern on the sand bed.

DOI： 10.1103/PhysRevE.96.062904

Web of Science

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

Helical carbon nanofibers (HCNFs) are spiral-shaped carbon nanofibers (CNFs) with coil and fiber diameters in the range of 500–1900 nm and 200–500 nm, respectively. The unique three-dimensional structure of HCNFs has induced many researchers to apply HNCFs in electronic engineering as well as mechanical engineering. HCNFs have been almost entirely grown using chemical vapor deposition with hydrocarbon feedstock gases. In this article, we review the history, classification, high-purity synthesis, and application of HCNFs.

DOI： 10.1016/j.mprp.2016.06.005

Scopus

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

We investigate the geometry of two-dimensional polygonal cracking that forms on the air-exposed surface of dried starch slurries. Two different kinds of starches, made from potato and corn, exhibited distinguished crack evolution, and there were contrasting effects of slurry thickness on the probability distribution of the polygonal cell area. The experimental findings are believed to result from the difference in the shape and size of starch grains, which strongly influence the capillary transport of water and tensile stress field that drives the polygonal cracking.

DOI： 10.1103/PhysRevE.96.023003

Web of Science

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

Bamboo exhibits unique structural properties that distinguish it from most other woody plants. One of the most remarkable properties is that the long hollow culm is separated into many small chambers by a sequence of nodes. The node distribution along the culm is, in general, sparse at the mid-culm and dense near the ends of the culm. In this study, we examined the intraspecific and interspecific variation in the node distribution of three species of the genus Phyllostachys (Phyllostachys pubescens Mazel ex Houz., Phyllostachys nigra var. henonis and Phyllostachys nigra Munro) with different culm sizes. The node distribution followed a single fitting curve via the normalization procedure, indicating the existence of a hidden universal law that governs the node distribution of the three species, despite their different appearances. Our findings also suggest that the node distribution along the mature culm could be determined at the stage of bamboo shoot by its base diameter.

DOI： 10.1007/s00468-017-1546-2

Web of Science

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

The optimal distribution of the reinforcing fibers for stiffening hollow cylindrical composites is explored using the linear elasticity theory. The spatial distribution of the vascular bundles in wild bamboo, a nature-designed functionally graded material, is the basis for the design. Our results suggest that wild bamboos maximize their flexural rigidity by optimally regulating the radial gradation of their vascular bundle distribution. This fact provides us with a plantmimetic design principle that enables the realization of high-stiffness and lightweight cylindrical composites.

DOI： 10.1371/journal.pone.0175029

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers S. V.  

We investigated whether the patterns of coordination that emerged during a three-participant (triadic) jumping task were defined by the symmetries of the (multi) agent-environment task space. Triads were instructed to jump around different geometrical arrangements of hoops. The symmetry of the hoop geometry was manipulated to create two symmetrical and two asymmetrical participant-hoop configurations. Video and motion tracking recordings were employed to determine the frequencies of coordination misses (collisions or failed jumps) and during 20 successful jump sequences, the jump direction chosen (clockwise vs. counterclockwise) and the patterning of between participant temporal movement lags within and across jump events. The results revealed that the (a)symmetry of the joint action workspace significantly influenced the (a)symmetry of the jump direction dynamics and, more importantly, the (a)symmetry of the between participant coordination lags. The symmetrical participant-hoop configurations resulted in smaller overall movement lags and a more spontaneous, interchangeable leader/follower relationship between participants, whereas the asymmetrical participant-hoop configurations resulted in slightly larger overall movements lags and a more explicit, persistent asymmetry in the leader/follower relationship of participants. The degree to which the patterns of behavioral coordination that emerged were consistent with the theory of symmetry groups and spontaneous and explicit symmetry-breaking are discussed.

DOI： 10.3389/fpsyg.2017.00003

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejam.72.I_25

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Dairy Science Association  

DOI： 10.11465/milk.65.161

CiNii Books

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications  

We carried out the atomistic structural instability (ASI) analysis with an empirical interatomic potential for carbon nanotubes (CNTs) under axial compression with the aim to reveal the mechanism of buckling. We investigated how ‘latent’ instability modes develop until one of them is activated at the structural instability. For pristine single-walled carbon nanotubes (SWCNTs), Euler-type buckling was found in relatively thin nanotubes, while buckling modes corresponding to change in the cross-sectional shape (radial buckling) were found in thick nanotubes. The crossover between the Euler-type buckling and radial buckling modes was clearly seen in the ASI analysis. While the reduction of Hessian eigenvalues in the pristine nanotubes and nanotubes with a vacancy is nearly linear until instability, rapid decrease of eigenvalues just before instability was found in models with Stone-Wales defects. This is due to localization of instability mode vectors around the defects that tends to arise before structural instability.

DOI： 10.4028/www.scientific.net/SSP.258.61

Scopus

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications  

This contribution provides simulated results of cross-sectional deformations observed in carbon nanotubes under high pressure. Molecular dynamics (MD) simulations were performed to explore radial buckling characteristics of multi-walled carbon nanotubes, and confirmed a variety of large-amplitude deformation modes. The energetically stable deformation mode turned out to be strongly dependent on the diameter of the innermost tube and the number of concentric walls. Critical buckling pressure obtained by MD simulations was compared with that estimated from a continuum elastic approximation, by which the validity of the continuum approximation was assessed.

DOI： 10.4028/www.scientific.net/SSP.258.65

Scopus

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

When two or more candle flames are fused by approaching them together, the resulting large flame often exhibits flickering, i.e., prolonged high-frequency oscillation in its size and luminance. In the present work, we investigate the collective behaviour of three-coupled candle flame oscillators in a triangular arrangement. The system showed four distinct types of syncronised modes as a consequence of spontaneous symmetry breaking. The modes obtained include the in-phase mode, the partial in-phase mode, the rotation mode, and an anomalous one called the "death" mode that causes a sudden stop of the flame oscillation followed by self-sustained stable combustion. We also clarified the correlation between the inter-flame distance and the frequency with which the modes occur.

DOI： 10.1038/srep36145

Web of Science

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

We investigate the low energy behavior of local density of states in metallic C-60 polymers theoretically. The multichannel bosonization method is applied to electronic band structures evaluated from first-principles calculation, by which the effects of electronic correlation and nanoscale corrugation in the atomic configuration are fully taken into account. We obtain a closed-form expression for the power-law anomalies in the local density of states, which successfully describes the experimental observation on the C-60 polymers in a quantitative manner. An important implication from the closed- form solution is the existence of an experimentally unobserved crossover at nearly a hundred milli-electron volts, beyond which the power-law exponent of the C-60 polymers should change significantly.

DOI： 10.1103/PhysRevB.93.165431

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

We have developed a precise resistivity measurement system for quasi-one-dimensional nanomaterials using a focused ion beam. The system enables the resistivity of carbon nanocoils (CNCs) to be measured and its dependence on coil geometry to be elucidated. At room temperature, the resistivity of CNCs tended to increase with coil diameter, while that of artificially graphitized CNCs remained constant. These contrasting behaviors indicate coil-diameter-induced enhancement in structural disorder internal to CNCs. Low-temperature resistivity measurements performed on the CNCs revealed that electron transport through the helical axis is governed by the variable range hopping mechanism. The characteristic temperature in variable range hopping theory was found to systematically increase with coil diameter, which supports our theory that the population of sp(2)-domains in CNCs decreases considerably with coil diameter. (C) 2016 AIP Publishing LLC.

DOI： 10.1063/1.4945724

Web of Science

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

Bamboo has a distinctive structure wherein a long cavity inside a cylindrical woody section is divided into many chambers by stiff diaphragms. The diaphragms are inserted at nodes and thought to serve as ring stiffeners for bamboo culms against the external load; if this is the case, the separation between adjacent nodes should be configured optimally in order to enhance the mechanical stability of the culms. Here, we reveal the hitherto unknown blueprint of the optimal node spacings used in the growth of wild bamboo. Measurement data analysis together with theoretical formulations suggest that wild bamboos effectively control their node spacings as well as other geometric parameters in accord with the lightweight and high-strength design concept.

DOI： 10.1103/PhysRevE.93.022406

Web of Science

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

The effect of fat content in cheese curds on their rheological properties was examined using dynamic shear measurements. Surplus fat addition to milk samples caused two distinct types of changes in the temperature dependence of the viscoelastic moduli of resultant curds. The first was a significant reduction in the moduli over a wide temperature range, which is attributed to the presence of liquefied fat globules within the milk protein network. The second was the excess contribution to the low-temperature moduli owing to the reinforcing effect of solidified fat globules. An upward shift in the sol-gel phase transition temperature driven by an increased fat content was also observed.

DOI： 10.1007/s00217-015-2525-8

Web of Science

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

Tensile tests were performed on nine carbon nanocoils (CNCs) using a focused-ion-beam (FIB) technique. In each experiment, an individual CNC was picked up using an FIB, and a CNC bridge formed between a tungsten probe and the spring-table substrate. Real-time observations of the CNC elongation and subsequent fracture under prolonged stretching enabled us to estimate the elastic limit, the spring constant, the shear modulus, and the ultimate strength of each CNC and their mean values. The mechanics of CNCs was also compared to that of macroscopic springs. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2014.11.034

Web of Science

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

Conversion of liquid milk to cheese curds is the first stage in cheese manufacture. Changing the rigidity of cheese curds through heating and pH control is an established method for preparing fresh curds, whereas a similar method to prepare fully coagulated curds is largely unknown. This study elucidated the effect of temperature variation on the viscoelastic moduli of fully coagulated curds under different pH conditions. The results showed that Rennet curds treated at pH 4.8 exhibited drastic changes in the viscoelasticity at 43 degrees C, above which the degree of fluidity exceeded the degree of rigidity. The viscoelastic moduli exhibited exponential decay as a function of temperature, which was independent of pH.

DOI： 10.1080/10942912.2014.978009

Web of Science

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

Molecular dynamics simulations of multiwalled carbon nanotubes under hydrostatic pressure are performed to elucidate the novel class of radial buckling in the systems. It is revealed by all-atom simulations that the initial circular cross section transforms into a flower-like wavy configuration at critical pressure on the order of hundreds mega pascals or less. This kind of radial buckling, called radial corrugation, originates from the competition of the three relevant energies in the system: in-plane strain energy, van der Waals interaction energy between adjacent tubes, and out-of-plane bending energy. Their possible consequences for physical properties of carbon nanotubes are also discussed.

DOI： 10.1080/15376494.2012.761303

Web of Science

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

We perform molecular dynamics simulations of a few-walled (with 3-4 walls) carbon nanotubes using empirical interatomic potential. We demonstrate that the radial corrugation occurs in such thin nanotubes under hydrostatic pressure, which is apparently similar to the corrugation in thicker (e.g., several tens-walled) nanotubes that had been predicted using continuum mechanics approximation. The mechanism underlying the corrugation of a few-walled nanotubes, however, is found to be much distinct from thick nanotubes; i.e., the sp(3) bonds between adjacent concentric walls and registry of atom arrangement take important roles in the formation and stabilization of corrugation modes in a few-walled nanotubes. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2014.09.010

Web of Science

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

This work focuses on a theoretical analysis of a well-known inertia demonstration, which uses a weight suspended by a string with an extra string that hangs below the weight. The point in question is which string, the upper or lower, will break when pulling down on the bottom edge of the lower string at a constant pulling speed. An analytic solution for the equation of motion allows us to identify the critical value of the pulling speed, beyond which the string breaking varies from one to the other. The analysis also provides us with a phase diagram that illustrates the interplay between the pulling speed and the string's elasticity in the pull-or-jerk experiment.

DOI： 10.1088/0143-0807/35/6/065016

Web of Science

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

When a straight hollow tube having circular cross-section is bent uniformly into an arc, the cross-section tends to ovalize or flatten due to the in-plane stresses induced by bending; this ovalization phenomenon is called the Brazier effect. The present paper is aimed at theoretical formulation of the Brazier effect observed in multilayered cylinders, in which a set of thin hollow cylinders are stacked concentrically about the common axis. The results indicate that mechanical couplings between stacked cylinders are found to yield pronounced suppression of the cross-sectional ovalization. Numerical computations have been performed to measure the degree of suppression in a quantitative manner and to explore how it is affected by the variations in the bending curvature, the number of stacked cylinders, and the interlayer coupling strength.

DOI： 10.1155/2014/923896

Web of Science

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

This article focuses on the analysis of cross-sectional deformations for single- and multi-walled carbon nanotubes using a molecular dynamics method. Carbon nanotubes consist of a graphene sheet (two-dimensional hexagonal lattices of carbon atoms) rolled up into a cylinder. This nanoscale structure has generated enormous interest in the research field of science and engineering in the last decades because of its excellent mechanical properties, such as extremely high elastic modulus and tensile strength. For example, the Young's modulus of nanotubes is estimated to be on the order of TPa (i.e., several times stiffer than steel) and the tensile strength is as high as tens of GPa. On the other hand, carbon nanotubes are known to have its remarkable flexibility when subjected to external hydrostatic pressure and bending force. Owing to such mechanical properties, they are regarded as an ideal material for superstrong nanofiber and thus hold great promise for use as next-generation materials. It has also been broadly accepted that mechanical deformation of a carbon nanotube causes significant changes in its physical and chemical properties. Precise knowledge of its deformation mechanism and available geometry is, therefore, crucial for understanding the precise physics and in developing nanotube-based applications. In earlier work, we carried out simulations based on the thin cylindrical shell theory to predict the occurrence of wavy-shaped carbon nanotubes, called "radial corrugation". However, the shell theory is valid only within linear elastic region, thus being unavailing for discussing large deformation behaviours beyond elastic approximation. Against the backdrop, we have performed molecular dynamics simulations to explore the post-buckled behavior in the cross-section of carbon nanotubes under high pressure. We have confirmed various deformation modes with large amplitude, in which the stable mode is strongly dependent on the tube diameter and the number of concentric walls.

DOI： 10.2208/jscejam.70.I_25

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

The multiplayer dynamics of a football game is analyzed to unveil self-similarities in the time evolution of player and ball positioning. Temporal fluctuations in both the team-turf boundary and the ball location are uncovered to follow the rules of fractional Brownian motion with a Hurst exponent of H similar to 0.7. The persistence time below which self-similarity holds is found to be several tens of seconds, implying a characteristic time scale that governs far-from-equilibrium motion on a playing field.

DOI： 10.1140/epjb/e2014-40987-5

Web of Science

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

We study ac electronic transport in semiconductor crystals with a screw dislocation. The screw dislocation in the crystal results in an effective potential field that has a pronounced effect on the quantum mechanical electronic transport of the system. Alternating current conductivity at a frequency around 100 GHz has been calculated, showing upward shift in the peak position with increasing the Fermi energy. The result is in contrast to the persistency in the peak position observed in a dislocation-free crystal penetrated by magnetic flux, despite the apparent similarity between the two crystalline systems. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2013.10.002

Web of Science

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本物理教育学会  

DOI： 10.20653/pesj.61.4_194

CiNii Books

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press  

DOI： 10.1017/jmech.2013.59

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：World Scientific  

Cross-sectional deformation of multiwalled carbon nanotubes under isotropic radial pressure is investigated in a realm of continuum elastic approximation. The nanotube we assumed is subjected to the embedment into an elastic medium and stiffener insertion into the core cavity. Combination of the two reinforcement manipulations is found to cause kaleidoscopic mode changes in the radial corrugation, in which the cylindrical walls exhibit wavy patterns along the circumferential direction. Physical consequences of the diverse corrugation patters are also discussed.

DOI： 10.1142/S0217979213501798

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Techno Press  

DOI： 10.12989/csm.2013.2.2.147

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Materials Research Society of Japan  

We theoretically demonstrate that the temperature (T)-dependence of photo-excited carrier relaxation time (τ) in energy-gapped systems strongly depends on the rate of energy transfer from a longitudinal to transverse acoustic phonon mode. By considering the anharmonic coupling between them, we resolve an ambiguity in how to interpret the T-dependence of τ in alkali-doped C₆₀ superconductors.

DOI： 10.14723/tmrsj.38.283

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

We elaborate on the cross-sectional deformation of carbon nanotubes embedded into a self-contracting host medium. The continuum elastic approach is used to formulate the mechanical energy of both the embedded nanotubes and the self-contracting outer medium with finite thickness. Our formula allows us to evaluate the critical radial pressure applied on the interface between the embedded nanotube and the outer contracting medium as well as the deformation mode that arises immediately above the critical pressure. An interesting mechanical implication of the embedding effect, that is, the power-law dependence of the critical pressure on the elastic modulus of the medium, is deduced by the theoretical approach established. © 2013 Motohiro Sato et al.

DOI： 10.1155/2013/767249

Scopus

Authorship：Last author   Language：Japanese   Publishing type：Research paper (research society, symposium materials, etc.)   Publisher：土木学会北海道支部  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (research society, symposium materials, etc.)   Publisher：土木学会北海道支部  

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Surface Science Society of Japan  

DOI： 10.1380/jsssj.34.9

CiNii Books

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

We develop a theory to describe the energy relaxation of photoexcited carriers in low-temperature ordered states with a band-gap opening. Carrier relaxation time tau near and below transition temperature T-c is formulated by examining the contributions from different carrier-phonon scatterings to the relaxation rate. Transverse acoustic phonon modes are found to play a crucial role in carrier relaxation; their heat capacity determines the tau divergence near T-c. Remarkable agreements with the theory and experimental data on two different materials which exhibit contrasting tau(T) behaviors are also demonstrated.

DOI： 10.1103/PhysRevB.86.104512

Web of Science

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

The tree-based rope swing is a popular recreational facility, often installed in outdoor areas. Hanging from a rope, users drop from a high platform and then swing at great speed like 'Tarzan', finally jumping ahead to land on the ground. The question naturally arises, how far can Tarzan jump using the swing? In this paper, I present an introductory analysis of the mechanics of the Tarzan swing, a large pendulum-like swing with Tarzan himself attached as weight. This enables determination of how much further forward Tarzan can jump using a given swing apparatus. The discussion is based on elementary mechanics and is, therefore, expected to provide rich opportunities for investigations using analytic and numerical methods.

DOI： 10.1088/0143-0807/33/6/1687

Web of Science

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

I consider the quantum interference of electrons moving along knotted trajectories under external magnetic field. The induced persistent current is formulated in terms of characteristic parameters that classify the torus knot geometry. The current is found to show a periodic oscillation whose period depends strongly both on the knot's class and the field direction. The shift in the oscillation period caused by geometric distortion is also discussed.

DOI： 10.1103/PhysRevB.86.035415

Web of Science

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

The critical buckling characteristics of hydrostatically pressurized complete spherical shells filled with an elastic medium are demonstrated. A model based on small deflection thin shell theory, the equations of which are solved in conjunction with variational principles, is presented. Axisymmetric and inextensional assumptions are not used initially in the exact formulation and the elastic medium is modelled as a Winkler foundation, i.e. using uncoupled radial springs with a constant foundation modulus that is independent of wave numbers of shell buckling modes. Simplified approximations based on a Rayleigh-Ritz approach are also introduced for the critical buckling pressure and the mode number with a considerable degree of accuracy. Characteristic modal shapes are demonstrated for a wide range of material and geometric parameters. A phase diagram is established to obtain the requisite thickness to radius, and stiffness ratios for a desired mode profile. The present exact formulation can be readily extended to apply to more general cases of non-axisymmetric buckling problems and the approximate method can be extended to the post-buckling range. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmecsci.2012.02.001

Web of Science

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

Einstein first applied Riemannian geometry to develop the general theory of relativity almost one hundred years ago and succeeded in understanding astronomical-scale phenomena such as the straining of time-space by a gravitational field. Whether or not Riemannian space affects the electronic properties of condensed matters on a much smaller scale is of great interest. Although Riemannian geometry has been applied to quantum mechanics since the 1950s, nobody has yet answered this question, because the electronic properties of materials with Riemannian geometry have not been examined experimentally. We report here the first observation of Riemannian geometrical effects on the electronic properties of materials such as Tomononaga-Luttinger liquids, which were previously theoretically predicted by our group. We present in situ high-resolution ultraviolet photoemission spectra of a one-dimensional metallic C-60 polymer with an uneven periodic peanut-shaped structure. Copyright (C) EPLA, 2012

DOI： 10.1209/0295-5075/98/27001

Web of Science

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

A one-dimensional (1D) uneven peanut-shaped C 60 polymer formed from electron-beam (EB)-induced polymerization of C 60 molecules showed an anomalous increase in two characteristic infrared (IR) peak intensities, which are respectively due to the radial and tangential motion of the 1D polymer, when compared to the IR peaks of pristine C 60 films. This anomaly was analyzed on the basis of the vibrational van Hove singularity (VHS), using an extended thin-shell elastic model fully considering the effects of periodic radius modulation inherent to the 1D uneven peanut-shaped C 60 polymer. We succeeded in explaining the enhancement in the tangential peak intensity by VHS, whereas the origin to cause that in the radial peak intensity is still unclear. © 2012 IOP Publishing Ltd.

DOI： 10.1088/0953-8984/24/17/175405

Web of Science

Scopus

PubMed

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

DOI： 10.4236/wjm.2012.21006

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

The radial deformation of multiwall carbon nanotubes (MWNTs) under hydrostatic pressure is investigated within the continuum elastic approximation. A thin-shell theory, with accurate elastic constants and interwall couplings, allows us to estimate the critical pressure above which the original circular cross-section transforms into radially corrugated ones. The emphasis is placed on the rigorous formulation of the van der Waals interaction between adjacent walls, which we analyze using two different approaches. Possible consequences of the radial corrugation in the physical properties of pressurized MWNTs are also discussed. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.commatsci.2011.04.005

Web of Science

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

The nonlinear mechanical response of carbon nanotubes, referred to as their buckling behavior, is a major topic in the nanotube research community. Buckling means a deformation process in which a large strain beyond a threshold causes an abrupt change in the strain energy vs. deformation profile. Thus far, much effort has been devoted to analysis of the buckling of nanotubes under various loading conditions: compression, bending, torsion, and their certain combinations. Such extensive studies have been motivated by (i) the structural resilience of nanotubes against buckling, and (ii) the substantial influence of buckling on their physical properties. In this contribution, I review the dramatic progress in nanotube buckling research during the past few years.

DOI： 10.3390/ma5010047

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

DOI： 10.2208/jscejam.67.I_15

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

The metal-semiconductor transition of peanut-shaped fullerene (C-60) polymers is clarified by considering the electron-phonon coupling in the uneven structure of the polymers. We established a theory that accounts for the transition temperature T-c reported in a recent experiment. The theory also suggests that T-c is considerably lowered by electron doping or prolonged irradiation during synthesis. The decrease in T-c is an appealing phenomenon with regard to realizing high-conductivity C-60-based nanowires even at low temperatures. Copyright (C) EPLA, 2011

DOI： 10.1209/0295-5075/96/27011

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Taylor Francis  

When a C60 film is irradiated with a 3 kV electron-beam in an ultrahigh vacuum (base pressure: 10-7 Pa), C60 molecules are coalesced to form a one-dimensional (1D) uneven peanut-shaped C60 polymer. From a topological viewpoint, since the polymer has both positive and negative Gaussian curvatures, it can be regarded as a new allotrope of nanocarbons different from graphene, fullerenes, and nanotubes. We will present our recent results of the electronic, optical, and electron-transport properties of the 1D uneven peanut-shaped C60 polymer and discuss its novel electronic properties on the basis of quantum mechanics in Riemannian space. © 2011 Taylor &amp
Francis Group, LLC.

DOI： 10.1080/1536383X.2011.586618

Scopus

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

We reformulate the Tomonaga-Luttinger liquid theory for quasi-one-dimensional Fermion systems with many subbands across the Fermi energy. Our theory enables us to obtain a rigorous expression of the local density of states (LDOS) for general multichannel quantum wires, describing how the power-law anomalies of the LDOS depend on inter- and intra-subbands couplings as well as the Fermi velocity of each band. The resulting formula for the exponents is valid in the cases of both bulk contact and edge contact, and thus plays a fundamental role in the physical properties of multicomponent Tomonaga-Luttinger liquid systems.

DOI： 10.1103/PhysRevB.84.075443

Web of Science

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

Electronic state modulation of armchair (6,6) carbon nanotubes filled with a linear assembly of oxygen molecules is addressed theoretically. Ferromagnetic ordering of encapsulated oxygen produces a magnetic field with cylindrical symmetry, which deviates the electron's eigenenergies from those prior to the oxygen absorption. An intriguing spectral gap arises near the Fermi energy, at which the gap formation is allowed only when the tube length equals to a multiple of three in units of carbon hexagon. A possible means to detect the selective gap formation is discussed. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2011.07.084

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

We reveal that the periodic radius modulation peculiar to one-dimensional (1D) peanut-shaped fullerene (C-60) polymers exerts a strong influence on their low-frequency phonon states and their interactions with mobile electrons. The continuum approximation is employed to show the zone-folding of phonon dispersion curves, which leads to fast relaxation of a radial breathing mode in the 1D C-60 polymers. We also formulate the electron-phonon interaction along the deformation potential theory, demonstrating that only a few set of electron and phonon modes yields a significant magnitude of the interaction relevant to the low-temperature physics of the system. The latter finding gives an important implication for the possible Peierls instability of the C-60 polymers suggested in the earlier experiment.

DOI： 10.1143/JPSJ.80.064704

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：World Scientific  

We investigate energetically favorable configurations of point disclinations in nematic films having a bump geometry. Gradual expansion in the bump width Delta gives rise to a sudden shift in the stable position of the disclinations from the top to the skirt of the bump. The positional shift observed across a threshold Delta(th) obeys a power law function of |Delta-Delta(th)|, indicating a new class of continuous phase transition that governs the defect configuration in curved nematic films.

DOI： 10.1142/S0217984911025912

Web of Science

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

DOI： doi.org/10.1140/epjb/e2010-10698-2

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

The coherent motion of electrons in a twisted quantum ring is considered to explore the effect of torsion inherent to the ring. Internal torsion of the ring composed of helical atomic configuration yields a non-trivial quantum phase shift in the electrons' eigenstates. This torsion-induced phase shift causes novel kinds of persistent current flow and an Aharonov-Bohm-like conductance oscillation. The two phenomena can occur even when no magnetic flux penetrates inside the twisted ring, thus being in complete contrast with the counterparts observed in untwisted rings. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1751-8113/43/35/354013

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

We investigate a correlation between the point disclination energies and the surface curvature modulation of nematic liquid crystal membranes with a Gaussian bump geometry. The correlation causes point disclinations to feel an attractive force that confines them to an annulus region, resulting in a halo distribution around the top of the bump. The halo formation is a direct consequence of the nonzero Gaussian curvature of the bump that affects preferable configurations of liquid crystal molecules around the disclination core.

DOI： 10.1143/JPSJ.79.074607

Web of Science

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

I consider the coarsening dynamics of two-dimensional dry foam sandwiched by deformable membranes. The time-varying deformation of the confining membranes gives rise to a significant alteration in the evolution of polygonal cells of bubbles when compared to the case of rigid membranes. This alteration is attributed to the correlation between the rate of inter-cell gas transfer and temporal fluctuation in surface curvature within a cell domain. Existing material constants are referred to show that the correlation can yield sizeable consequences in actual coarsening experiments. © 2010 The Physical Society of Japan.

DOI： 10.1143/JPSJ.79.074601

Scopus

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

A novel conductance oscillation in a twisted quantum ring composed of a helical atomic configuration is theoretically predicted. The internal torsion of the ring is found to cause a quantum phase shift in the wavefunction that describes the electron's motion along the ring. The resulting conductance oscillation is free from magnetic flux penetrating inside the ring, which is in complete contrast with the case for the ordinary Aharonov-Bohm effect observed in untwisted quantum rings.

DOI： 10.1088/0953-8984/22/24/245302

Web of Science

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

We investigate surface-curvature induced alteration in the Tomonaga-Luttinger liquid (TLL) states of a one-dimensional (1D) deformed hollow nanotube with a dumbbell-shape. Periodic variation of the surface curvature along the axial direction is found to enhance the TLL exponent significantly, which is attributed to an effective potential field that acts low-energy electrons moving on the curved surface. The present results accounts for the experimental observation of the TLL properties of 1D metallic peanut-shaped fullerene polymers whose enveloping surface is assumed to be a dumbbell-shaped hollow tube. (c) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2009.10.030

Web of Science

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

Effects of periodic curvature on the electrical resistivity of corrugated semiconductor films are theoretically considered. The presence of a curvature-induced potential affects the motion of electrons confined to the thin curved film, resulting in a significant resistivity enhancement at specific values of two geometric parameters: the amplitude and period of the surface corrugation. The maximal values of the two parameters in order to observe the corrugation-induced resistivity enhancement in actual experiments are quantified by employing existing material constants. (c) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2009.11.103

Web of Science

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

We describe the effects of geometric torsion on the coherent motion of electrons along a thin twisted quantum ring. The geometric torsion inherent in the quantum ring triggers a quantum phase shift in the electrons' eigenstates, thereby resulting in a torsion-induced persistent current that flows along the twisted quantum ring. The physical conditions required for detecting the current flow are discussed.

DOI： 10.1088/0953-8984/22/7/075301

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：World Scientific  

The present paper investigates the cross-sectional morphology of Multiwalled Carbon Nanotubes (MWNTs) restrained radially and circumferentially by an infinite surrounding elastic medium, subjected to uniform external hydrostatic pressure. In this study, a two-dimensional plane strain model is developed, assuming no variation of load and deformation along the tube axis. We find some characteristic cross-sectional shapes from the elastic buckling analysis. The effect of the surrounded elastic medium on the cross-sectional shape which occurs due to pressure buckling is focused on by the comparison with the shape for no elastic medium case in our discussion. It is suggested that in no embedded elastic medium cases, the cross-sectional shapes of inner tubes maintain circle or oval; on the other hand, an embedded medium may cause inner tube corrugation modes especially when the number of shells for MWNTs is small.

DOI： 10.1142/S0217979210064228

Web of Science

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

Stable cross sections of multiwalled carbon nanotubes subjected to electron-beam irradiation are investigated in the realm of the continuum mechanics approximation. The self-healing nature of s p2 graphitic sheets implies that selective irradiation of the outermost walls causes their radial shrinkage with the remaining inner walls undamaged. The shrinking walls exert high pressure on the interior part of nanotubes, yielding a wide variety of radial-corrugation patterns (i.e., circumferentially wrinkling structures) in the cross section. All corrugation patterns can be classified into two deformation phases for which the corrugation amplitudes of the innermost wall differ significantly. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.82.085401

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：土木学会  

J-GLOBAL

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

We study the q-state clock models on heptagonal lattices assigned on a negatively curved surface. We show that the system exhibits three classes of equilibrium phases
in between ordered and disordered phases, an intermediate phase characterized by a diverging susceptibility with no magnetic order is observed at every q≥2. The persistence of the third phase for all q is in contrast with the disappearance of the counterpart phase in a planar system for small q, which indicates the significance of nonvanishing surface-volume ratio that is peculiar in the heptagonal lattice. Analytic arguments based on Ginzburg-Landau theory and generalized Cayley trees make clear that the two-stage transition in the present system is attributed to an energy gap of spin-wave excitations and strong boundary-spin contributions. We further demonstrate that boundary effects break the mean-field character in the bulk region, which establishes the consistency with results of clock models on boundary-free hyperbolic lattices. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevE.80.011133

Scopus

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

We demonstrate a novel cross-sectional deformation, called the radial corrugation, of multi-walled carbon nanotubes (MWNTs) under hydrostatic pressure. Theoretical analyses based on the continuum elastic approximation have revealed that MWNTs consisting of more than ten concentric walls undergo elastic deformations at critical pressure p(c) similar or equal to 1 GPa, above which the circular shape of the cross-section becomes radially corrugated. Various corrugation modes have been observed by tuning the innermost tube diameter and the number of constituent walls, which is a direct consequence of the core-shell structure of MWNTs.
[GRAPHICS]
Cross-sectional views of MWNT under high hydrostatic pressure: elliptic deformation with the mode index n = 2 (left), and radial corrugations with n = 5 (center), and n = 6 (right). The index it indicates the circumferential wave number of the deformed cross-section. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssa.200881706

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We study low-temperature properties of the XY spin model on a negatively curved surface. Geometric curvature of the surface gives rise to frustration in local spin configuration, which results in the formation of high-energy spin clusters scattered over the system. Asymptotic behavior of the spin-glass susceptibility suggests a zero-temperature glass transition, which is attributed to multiple optimal configurations of spin clusters due to nonzero surface curvature of the system. It implies that a constant ferromagnetic spin interaction on a regular lattice can exhibit glasslike behavior without possessing any disorder if the lattice is put on top of a negatively curved space such as a hyperbolic surface.

DOI： 10.1103/PhysRevE.79.060106

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The low-temperature electrical resistivity of corrugated semiconductor films is theoretically considered. Nanoscale corrugation enhances the electron-electron scattering contribution to the resistivity resulting in a stepwise resistivity development with increasing corrugation amplitude. The enhanced electron scattering is attributed to the curvature-induced potential energy that affects the motion of electrons confined to a thin curved film. Geometric conditions and microscopic mechanism of the stepwise resistivity are discussed in detail. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.79.235407

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Techno Press  

DOI： 10.12989/imm.2009.2.2.209

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

We demonstrate the effects of geometric perturbation on the Tomonaga-Luttinger liquid (TLL) states in a long, thin, and hollow cylinder whose radius varies periodically. The variation in the surface curvature inherent to the system gives rise to a significant increase in the power-law exponent of the single- particle density of states. The increase in the TLL exponent is caused by a curvature-induced potential that attracts low-energy electrons to region that has large curvature. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.79.201401

Web of Science

Scopus

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We examine the ordering behavior of the ferromagnetic Ising lattice model defined on a surface with a constant negative curvature. Small-sized ferromagnetic domains are observed to exist at temperatures far greater than the critical temperature, at which the inner-core region of the lattice undergoes a mean-field phase transition. The survival of short-range order at such high temperatures can be attributed to strong boundary-spin contributions to the ordering mechanism as a result of which boundary effects remain active even within the thermodynamic limit. Our results are consistent with the previous finding of disorder-free Griffiths phase that is stable at temperatures lower than the mean-field critical temperature. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevE.80.021103

Scopus

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We investigate localization properties of one-dimensional electronic systems with long-range correlated disorders characterized by a power-law spectral density. An abrupt change from extended to gradon states is found to occur in individual samples independently of system sizes. This abrupt change differs from the ordinary Anderson transition in the sense that the former accompanies strong sample fluctuations that remain significant even in the thermodynamic limit. We further observe that sample-averaged quantities such as the inverse participation ratio and the level-spacing distribution exhibit nontrivial crossover behaviors from extended states to gradon states.

DOI： 10.1103/PhysRevB.79.033105

Web of Science

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

Radial elastic corrugation of multiwalled carbon nanotubes under hydrostatic pressure is demonstrated by using the continuum elastic theory. Various corrugation patterns are observed under a pressure of several GPa, wherein the stable cross-sectional shape depends on the innermost tube diameter D and the total number N of concentric walls. A phase diagram is established to obtain the requisite values of D and N for a desired corrugation pattern among choices. In all corrugation patterns, the cylindrical symmetry of the innermost tube is maintained even under high external pressure.

DOI： 10.1088/0957-4484/19/49/495705

Web of Science

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

We demonstrate the nontrivial scaling behavior of Ising models defined on (i) a donut-shaped surface and (ii) a curved surface with a constant negative curvature. By performing Monte Carlo simulations, we find that the former model has two distinct critical temperatures at which both the specific heat C(T) and magnetic susceptibility chi(T) show sharp peaks. The critical exponents associated with the two critical temperatures are evaluated by the finite-size scaling analysis; the result reveals that the values of these exponents vary depending on the temperature range under consideration. In the case of the latter model, it is found that static and dynamic critical exponents deviate from those of the Ising model on a flat plane; this is a direct consequence of the constant negative curvature of the underlying surface. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.207

Web of Science

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

The curvature effect on the electronic states of a deformed cylindrical conducting surface of variable diameter is theoretically investigated. The quantum confinement of electrons normal to the curved surface results in an effective potential energy that affects the electronic structures of the system at low-energies. This suggests the possibility that ballistic transport of electrons in low-dimensional nanostructures can be controlled by inducing a local geometric deformation. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.220

Web of Science

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

DOI： 10.1016/j.cpc.2007.02.016

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier  

The localization behaviors of harmonic chains with correlated random masses are theoretically investigated. We show that the specific long-range correlation in a mass sequence gives rise to the occurrence of peculiar localized eigenmodes at high frequencies as well as an anomalous behavior in level statistics in vibrational spectrum.

DOI： 10.1088/1742-6596/92/1/012156

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier  

Effects of the surface curvature on the electronic states of a cylindrical conducting surface with a variable diameter are theoretically investigated. The quantum confinement of electrons normal to the curved surface results in an effective potential energy that affects the electronic structures of the system at low energies. This suggests the possibility of controlling the electric conductivity of low-dimensional nanostructures by inducing a local geometric deformation.

DOI： 10.1088/1742-6596/61/1/226

Web of Science

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

We have considered critical properties of the heptagonal and triangular Ising lattice models defined on negatively curved surfaces. Finite-size scaling analyze reveal that several critical exponents take values distinct from those for the two-dimensional Ising model on a flat plane. This deviation originates from non-Euclidean property of the curved surface that leads to an alteration in global symmetries of the mounted system. Besides, it indicates the occurrence of a novel universality class of the Ising model induced by negative surface curvature. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.418

Web of Science

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

We investigate the dynamic critical exponent of a two-dimensional Ising model defined on a curved surface with a constant negative curvature. By means of the short-time relaxation method, we find that a non-zero curvature of the underlying surface engenders a quantitative alternation of the dynamic exponent from the known value for the planar Ising model. This indicates the occurrence of a novel dynamic universality class of the Ising model induced by the negative surface curvature. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.416

Web of Science

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

We have investigated critical behavior of the Ising lattice model assigned on a donut-shaped surface. By means of Monte Carlo simulations, we have found that the model exhibits two distinct critical temperatures at which zero-field magnetic susceptibility show sharp peaks. This peculiarity is attributed to a spatially non-uniform distribution of the Ising spins on-the donut surface. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.423

Web of Science

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

We investigate the dynamic critical exponent of the two-dimensional Ising model defined on a curved surface with constant negative curvature. By using the short-time relaxation method, we find a quantitative alteration of the dynamic exponent from the known value for the planar Ising model. This phenomenon is attributed to the fact that the Ising lattices embedded on negatively curved surfaces act as ones in infinite dimensions, thus yielding the dynamic exponent deduced from mean field theory. We further demonstrate that the static critical exponent for the correlation length exhibits the mean field exponent, which agrees with the existing results obtained from canonical Monte Carlo simulations.

DOI： 10.1088/1742-5468/2006/08/P08017

Web of Science

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

We investigate the critical behaviour of the two-dimensional Ising model defined on a curved surface with a constant negative curvature. Finite-size scaling analysis reveals that the critical exponents for the zero-field magnetic susceptibility and the correlation length deviate from those for the Ising lattice model on a flat plane. Furthermore, when reducing the effects of boundary spins, the values of the critical exponents tend to those derived from the mean field theory. These findings evidence that the underlying geometric character is responsible for the critical properties of the Ising model when the lattice is embedded on negatively curved surfaces. © 2006 IOP Publishing Ltd.

DOI： 10.1088/0305-4470/39/18/010

Web of Science

Scopus

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

We address the accurate treatment of dipolar interaction effects between oxygen defects in Ge crystals on the low-temperature properties of bulk systems. On the basis of a quantum rotor model, we reveal that the interaction between adjacent oxygen defects generates nontrivial low-lying excitations that result in power-law specific heats below 0.1 K. In addition, a peculiar hump is observed for the dielectric susceptibilities at approximately I K. Further, we contend that the predicted power-law specific heats are well described by the two-level tunneling theory, which is based on the random distribution of interacting oxygen defects in Ge samples. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.042

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We investigate the interaction effect between oxygen impurities in crystalline germanium on the basis of a quantum rotor model. The dipolar interaction of nearby oxygen impurities engenders nontrivial low-lying excitations, giving rise to anomalous behaviors for oxygen-doped germanium (Ge:O) below a few degrees Kelvin. In particular, it is theoretically predicted that Ge:O samples with oxygen-concentration of 10(17-18) cm(-3) show (i) power-law specific heats below 0.1 K, and (ii) a peculiar hump in dielectric susceptibilities around 1 K. We present an interpretation for the power-law specific heats, which is based on the picture of local double-well potentials randomly distributed in Ge:O samples.

DOI： 10.1103/PhysRevB.71.155210

Web of Science

Scopus

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

We investigate the quantum dynamics of interacting polar molecules under the application of a short laser pulse. It is elucidated by numerical simulations that the field-free orientation of interacting molecules is remarkably enhanced by magnifying dipolar interaction between the molecules. This enhanced orientation is purely a quantum effect since dipolar interaction between molecules prevents a post-pulsed orientation within the classical limit. We also reveal that a specially designed sequence of pulses can most efficiently enhance the orientation of interacting molecules. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.mejo.2005.02.115

Web of Science

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

The localization properties of one-dimensional (1D) electron systems subject with long-range correlated diagonal disorder are investigated. Numerical simulations elucidate the existence of the localization-delocalization transition in 1D systems, which is contrary to the conclusions of the well-known scaling theory. The values of the critical exponent v in the case of the localization length of eigenstates is determined by employing the finite-size scaling analysis, revealing that all values of v disobey the Harris criterion v > 2/d. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.mejo.2005.02.037

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

The low-temperature properties of crystalline germanium with oxygen impurities (Ge:O) are theoretically investigated in terms of the quantum rotor model. We predict that Ge:O samples with oxygen-impurity concentration of 10(17)-10(18) cm(-3) show anomalous temperature dependences for specific heat and dielectric susceptibility below 1 K. These peculiar properties of Ge:O originate from the correlated motion of paired-rotors coupled via dipolar interactions.

DOI： 10.1143/JPSJ.73.2464

Web of Science

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

We investigate localization properties of electron eigenstates in one-dimensional (1D) systems with long-range correlated diagonal disorder. Numerical studies on the localization length xi of eigenstates demonstrate the existence of the localization-delocalization transition in 1D systems and elucidate nontrivial behavior of xi as a function of the disorder strength. The critical exponent nu for localization length is extracted for various values of parameters characterizing the disorder, revealing that every nu disobeys the Harris criterion nu>2/d.

DOI： 10.1103/PhysRevB.70.075116

Web of Science

Scopus

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

We pointed out that the nonadiabatic orientation of quantum rotors, produced by ultrashort laser pulses, is remarkably enhanced by introducing dipolar interaction between the rotors. This enhanced orientation of quantum rotors is in contrast with the behavior of classical paired rotors, in which dipolar interactions prevent the orientation of the rotors. We demonstrate also that a specially designed sequence of pulses can most efficiently enhance the orientation of quantum paired rotors.

DOI： 10.1103/PhysRevA.70.013401

Web of Science

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

The correlated dynamics of coupled quantum rotors carrying electric dipole moment is theoretically investigated. The energy spectra of coupled rotors as a function of dipolar interaction energy are analytically solved. The calculated dielectric susceptibilities of the system show a peculiar temperature dependence different from that of isolated rotors.

DOI： 10.1103/PhysRevB.69.035202

Web of Science

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

The forced oscillator method is a powerful algorithm to calculate physical quantities of the system described by very large Hamiltonian matrices. The efficiency of this algorithm is greatly enhanced by combining the fast time-evolution method. The article gives a description of these numerical methods, including its applications to a model for three-dimensional network glasses. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)00560-4

Web of Science

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

The forced oscillator method (FOM) is a powerful algorithm to calculate linear response functions of quantum systems represented by very large Hamiltonian matrices. We demonstrate the efficiency of the FOM by applying for the calculation of the ac conductivity sigma(omega) for two-dimensional electron systems with spin-orbit interactions. for which conventional numerical methods are inoperative. It is shown that the efficiency of the FOM is greatly enhanced by combining the fast time-evolution method. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0010-4655(01)00379-4

Web of Science

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

The frequency dependence of the ac conductivity for a two-dimensional electron system subject to a long-range random magnetic field (RMF) with zero mean is numerically investigated. It is found that the ac conductivity (Tuv) increases in the frequency regime lower than a crossover frequency omega(c) and linearly decreases for to omega much greater than omega(c). The crossover frequency is governed by the localization length of the electron eigenstate at the Fermi energy. These facts indicate that quantum-interference effects are crucial for ac transport in the long-range RMF in conflict with the recent analytical argument. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0010-4655(01)00382-4

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

We numerically stud's the spatial profiles of wavefunctions and the frequency dependences of the ac conductivity sigma(omega) for two-dimensional electron systems subject to long-range random magnetic fields (RMF) with zero mean. It ib found, for a weak RMF. that amplitudes of the wavefunction are almost uniformly distributed over the system, and the ac conductivity, is described by, the Drude theory Under a strong RMF, quantum states corresponding to classical snake trajectories can be strongly localized, which implies that the quantum interference along zero magnetic field contours is crucial for understanding electron transport. In this case, the conductivity sigma(omega) rapidly increases in the frequency regime lower than a crossover frequency omega (c) and decreases linearly omega much greater than omega (c). The crossover frequency is governed the localization length of the electron eigenstate at the Fermi energy.

DOI： 10.1143/JPSJ.70.2682

Web of Science

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

The AC conductivity of a two-dimensional electron system subject to a long-range random magnetic field (RMF) with zero mean is numerically investigated. The AC conductivity σ(ω) increases at frequencies lower than a crossover frequency ωc, and linearly decreases for ω ≫ ωc. The crossover frequency ωc is governed by the localization length of the electron eigenstate at the Fermi energy. These results indicate that quantum interference effects are crucial for AC transport in a long-range RMF, which conflicts with a recent analytical argument. © 2001 Elsevier Science B.V.

DOI： 10.1016/S0921-4526(01)00263-0

Scopus

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

The dynamic scaling behavior of ac conductivity sigma(omega) proportional to omega(delta)(delta similar or equal to 1/3) in three dimensional (3D) systems is investigated by means of the forced oscillator method (FOM). The exponents delta for various universality classes are determined by the finite-time scaling approach.

DOI： 10.1143/PTPS.138.515

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We investigate the dynamic scaling behavior of ac conductivity sigma(omega) in three-dimensional (3D) unitary and symplectic systems in addition to orthogonal one by means of large-scale simulations. It is demonstrated that the ac conductivity near the Anderson transition behave as sigma(omega)proportional to omega(delta)(delta similar or equal to 1/3) for all of the above systems. Numerical calculations are performed by an efficient algorithm based on the forced oscillator method (FOM), which enables us to accurately treat large-scale quantum systems with less computational effort. The values of the exponents delta are determined by the finite-time scaling method for the FOM. [S0163-1829(99)11943-X].

DOI： 10.1103/PhysRevB.60.14066

Web of Science

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

DOI： 10.1103/PhysRevE.58.3984

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

It is demonstrated that the finite-time scaling approach, derived from the forced oscillator method, to determine the exponent of the ac conductivity σ(ω) ∝ ωδ near the metal-insulator transition point is a very powerful method for evaluating the precise value of the exponent δ with high speed and accuracy. © 1998, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.67.2189

Scopus

Responsible for pages：-   Language：English  

Responsible for pages：-   Language：English  

Responsible for pages：-   Language：English  

Responsible for pages：100-105   Language：Japanese  

Language：Japanese   Book type：Scholarly book

Language：English   Book type：Scholarly book

Responsible for pages：-   Language：English  

ISBN: 978-148222301-9

Responsible for pages：-   Language：English  

Responsible for pages：-   Language：English  

Total pages：240   Responsible for pages：-   Language：English  

ISBN: 978-981431075-8

Responsible for pages：-   Language：English  

ISBN: 978-098695542-6

Responsible for pages：100-105   Language：Japanese  

Total pages：702   Responsible for pages：-   Language：English  

ISBN: 978-354087863-6

Event date： 2023.3

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Event date： 2022.10

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Venue：同志社大学・京田辺キャンパス  

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Event date： 2018.8

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Venue：University of Yamanashi  

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Event date： 2018.7

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Event date： 2018.6

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Venue：東北大学 青葉山東キャンパス  

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Venue：東北大学 青葉山東キャンパス  

Event date： 2018.6

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Venue：ウインクあいち  

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Venue：ウインクあいち  

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Venue：横浜国立大学  

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Venue：横浜国立大学  

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Venue：東京ビックサイト  

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Venue：北海道大学