IOP Publishing Acta Medica Okayama 1882-0778 18 10 2025 Multichannel topological elastic waveguide in a multilayer Kagome phononic crystal 107001 EN Yusuke Hata Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University By examining the geometric characteristics of various boundaries formed within the Kagome phononic lattice and vertically stacking the lattices, we designed an elastic waveguide that enables selective propagation of topologically protected edge modes across layers in a bilayer system. This layer-selective transmission is manifested as polarized boundary modes that appear in phononic dispersions of the systems incorporating the bridge, zigzag, and armchair boundaries. We numerically demonstrated that efficient elastic layer converters and splitters can be designed, thereby paving the way for the practical development of three-dimensional elastic-wave devices. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2041-1723 15 1 2024 Photoinduced dynamics during electronic transfer from narrow to wide bandgap layers in one-dimensional heterostructured materials 4600 EN Yuri Saida Graduate School of Science and Technology, University of Tsukuba Thomas Gauthier Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) UMR 6251 Hiroo Suzuki Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Satoshi Ohmura Faculty of Engineering, Hiroshima Institute of Technology Ryo Shikata Graduate School of Science and Technology, University of Tsukuba Yui Iwasaki Graduate School of Science and Technology, University of Tsukuba Godai Noyama Graduate School of Science and Technology, University of Tsukuba Misaki Kishibuchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Yuichiro Tanaka Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Wataru Yajima Graduate School of Science and Technology, University of Tsukuba Nicolas Godin Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) UMR 6251 Gael Privault Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) UMR 6251 Tomoharu Tokunaga Graduate School of Engineering, Nagoya University Shota Ono Institute for Materials Research, Tohoku University Shin-Ya Koshihara School of Science, Tokyo Institute of Technology Kenji Tsuruta Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Yasuhiko Hayashi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Roman Bertoni Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) UMR 6251 Masaki Hada Institute of Pure and Applied Science and Tsukuba Research Center for Energy Materials Science (TREMS), University of Tsukuba Electron transfer is a fundamental energy conversion process widely present in synthetic, industrial, and natural systems. Understanding the electron transfer process is important to exploit the uniqueness of the low-dimensional van der Waals (vdW) heterostructures because interlayer electron transfer produces the function of this class of material. Here, we show the occurrence of an electron transfer process in one-dimensional layer-stacking of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs). This observation makes use of femtosecond broadband optical spectroscopy, ultrafast time-resolved electron diffraction, and first-principles theoretical calculations. These results reveal that near-ultraviolet photoexcitation induces an electron transfer from the conduction bands of CNT to BNNT layers via electronic decay channels. This physical process subsequently generates radial phonons in the one-dimensional vdW heterostructure material. The gathered insights unveil the fundamentals physics of interfacial interactions in low dimensional vdW heterostructures and their photoinduced dynamics, pushing their limits for photoactive multifunctional applications. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 1882-0778 16 9 2023 Active control of localized mode and transmission in topological phononic waveguides by non-Hermitian modulation 094001 EN Md. Shuzon Ali Department of Electrical and Electronic Engineering, Okayama University Yusuke Hata Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University We demonstrate the switching behavioral differences between lossy and nearly lossless edge-mode propagation by non-Hermitian modulation based on the phononic band design of a C3v symmetric, two-dimensional phononic crystal with a unit cell composed of three air-filled circular holes in polydimethylsiloxane. We numerically show that strong loss effects lead to the extinction of the localized modes. This mechanism is analogous to the bound-to-unbound transition in non-Hermitian quantum systems. This result suggests that large variations in non-Hermitian modulation can be used for the active control of edge-mode propagation along topological interfaces. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0021-4922 62 SJ 2023 Reconfigurable waveguide based on valley topological phononic crystals with local symmetry inversion via continuous translation SJ1002 EN Md. Shuzon Ali Department of Electrical and Electronic Engineering, Okayama University Motoki Kataoka Department of Electrical and Electronic Engineering, Okayama University Masaaki Misawa Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University We proposed a reconfigurable valley topological acoustic waveguide constructed using a 2D phononic crystal (PnC) with C3v symmetric arrangement of three rods in the unit cell. An interface between two types of PnCs with differently oriented unit cells exhibits high robustness of the valley transport of acoustic waves via the topologically protected state. Structural reconfiguration was introduced by the continuous translation of rod arrays in the PnCs. The topological phase transition in this translational change was quantitatively identified by the change in the Berry curvature. The translation of the rods leaves a dimer array at the interface, creating a localized/defective mode along the waveguide. Despite the presence of the localized mode, the acoustic wave can propagate along the reconfigurable waveguide the same as the original waveguide. The continuous translation of a rod array can be used to turn on and off the bandgap. This can be a new approach to design a robust acoustic device with a high reconfigurability. No potential conflict of interest relevant to this article was reported.

The Japan Society of Vacuum and Surface Science Acta Medica Okayama 1348-0391 20 4 2022 First-principles Analysis of Stearic Acid Adsorption on Calcite (104) Surface 261 265 EN Narumi Machida Graduate School of Natural Science and Technology, Okayama University Masaaki Misawa Faculty of Natural Science and Technology, Okayama University Yuki Kezuka Shiraishi Central Laboratories Co., Ltd. Kenji Tsuruta Faculty of Natural Science and Technology, Okayama University Calcium carbonate nanoparticles are often surface-treated with organic compounds such as fatty acids. The activated calcium carbonates not only exhibit excellent application properties, but also can be applied as eco-friendly inorganic-organic hybrid materials. However, the microscopic adsorption structure of organic compounds on calcite surfaces is not yet well understood. In this study, we performed computational simulations based on density functional theory to investigate adsorption states of stearic acid (SA) on a calcite (104) surface. Based on the first-principles ionic relaxation and molecular dynamics simulations for several types of SA－SA and calcite－SA bonding models, a SA bilayer model on the calcite (104) surface is predicted to be a possible stable structure. The proposed structure model is well consistent with the experimentally predicted adsorption mechanism of SA on the calcite (104) surface. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0021-4922 62 SJ 2023 Acoustic metasurfaces and topological phononics for acoustic/elastic device design SJ0803 EN Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University This paper reviews recent progress in acoustic metasurfaces and the novel concept of "topological acoustic/phononics" for designing compact yet efficient acoustic devices. After a brief review of this research area and its impact on ultrasonic technologies, some of the efforts to develop highly efficient sound absorption devices using acoustic metasurfaces are introduced. A resonance-based mechanism to achieve efficient absorption in metasurface structures thinner than the wavelength of the incident sound is briefly discussed, and its extensions to a broad spectrum are highlighted. Next, a valley topological phononic system is introduced, and its applications to the design of phononic waveguides are exemplified. The band structure design for extracting topologically protected edge modes is shown together with a numerical and experimental demonstration of the robustness of phononic waveguides constructed in both acoustic and elastic regimes. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2073-8994 14 10 2022 Design and Robustness Evaluation of Valley Topological Elastic Wave Propagation in a Thin Plate with Phononic Structure 2133 EN Motoki Kataoka Department of Electrical and Electronic Engineering, Okayama University Masaaki Misawa Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University Based on the concept of band topology in phonon dispersion, we designed a topological phononic crystal in a thin plate for developing an efficient elastic waveguide. Despite that various topological phononic structures have been actively proposed, a quantitative design strategy of the phononic band and its robustness assessment in an elastic regime are still missing, hampering the realization of topological acoustic devices. We adopted a snowflake-like structure for the crystal unit cell and determined the optimal structure that exhibited the topological phase transition of the planar phononic crystal by changing the unit cell structure. The bandgap width could be adjusted by varying the length of the snow-side branch, and a topological phase transition occurred in the unit cell structure with threefold rotational symmetry. Elastic waveguides based on edge modes appearing at interfaces between crystals with different band topologies were designed, and their transmission efficiencies were evaluated numerically and experimentally. The results demonstrate the robustness of the elastic wave propagation in thin plates. Moreover, we experimentally estimated the backscattering length, which measures the robustness of the topologically protected propagating states against structural inhomogeneities. The results quantitatively indicated that degradation of the immunization against the backscattering occurs predominantly at the corners in the waveguides, indicating that the edge mode observed is a relatively weak topological state. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0021-4922 60 SD 2021 Low-frequency sound absorbing metasurface using multilayer split resonators SDDA01 EN Shota Takasugi Department of Electrical and Electronic Engineering, Okayama University Keita Watanabe Department of Electrical and Electronic Engineering, Okayama University Masaaki Misawa Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University Among the acoustic metasurfaces that can control the propagation of sound waves with the structure far thinner than the wavelength at the operating frequency, the split tube structure has shown its effectiveness in the lower frequency band. Here we focus on multiply layered split tubes to broaden the absorption spectrum. By numerical analysis, we show up-to six-layer structure possessing wideband (1–1000 Hz) sound absorption. The absorbing peaks in the frequency band below 1000 Hz are shown to be multiplexed not only by simple superposition of vibrational modes of each layer, but also by hybridization of the modes indicating collective motion of tubes. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 0003-6951 117 10 2020 Super-chiral vibrational spectroscopy with metasurfaces for high-sensitive identification of alanine enantiomers 101103 EN Takumi Iida Department of Electrical and Electronic Engineering, Okayama University Atsushi Ishikawa Department of Electrical and Electronic Engineering, Okayama University Takuo Tanaka Metamaterials Laboratory, RIKEN Cluster for Pioneering Research Atsuya Muranaka Advanced Elements Chemistry Laboratory, RIKEN Cluster for Pioneering Research Masanobu Uchiyama Advanced Elements Chemistry Laboratory, RIKEN Cluster for Pioneering Research Yasuhiko Hayashi Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University Chiral nature of an enantiomer can be characterized by circular dichroism (CD) spectroscopy, but such a technique usually suffers from weak signal even with a sophisticated optical instrument. Recent demonstrations of plasmonic metasurfaces showed that chiroptical interaction of molecules can be engineered, thereby greatly simplifying a measurement system with high sensing capability. Here, by exploiting super-chiral field in a metasurface, we experimentally demonstrate high-sensitive vibrational CD spectroscopy of alanine enantiomers, the smallest chiral amino acid. Under linearly polarized excitation, the metasurface consisting of an array of staggered Au nano-rods selectively produces the left- and right-handed super-chiral fields at 1600 cm－1, which spectrally overlaps with the functional group vibrations of alanine. In the Fourier-transform infrared spectrometer measurements, the mirror symmetric CD spectra of D- and L-alanine are clearly observed depending on the handedness of the metasurface, realizing the reliable identification of small chiral molecules. The corresponding numerical simulations reveal the underlying resonant chiroptical interaction of plasmonic modes of the metasurface and vibrational modes of alanine. Our approach demonstrates a high-sensitive vibrational CD spectroscopic technique, opening up a reliable chiral sensing platform for advanced infrared inspection technologies. No potential conflict of interest relevant to this article was reported.

Nature Acta Medica Okayama 2045-2322 10 1 2020 Whitish daytime radiative cooling using diffuse reflection of non-resonant silica nanoshells 6486 EN Takahiro Suichi Department of Electrical and Electronic Engineering, Okayama University Atsushi Ishikawa Department of Electrical and Electronic Engineering, Okayama University Takuo Tanaka Metamaterials Laboratory, RIKEN Cluster for Pioneering Research Yasuhiko Hayashi Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University Daytime radiative cooling offers efficient passive cooling of objects by tailoring their spectral responses, holding great promise for green photonics applications. A specular reflector has been utilized in cooling devices to minimize sunlight absorption, but such a glaring surface is visually less appealing, thus undesirable for public use. Here, by exploiting strong diffuse reflection of silica nanoshells in a polymer matrix, daytime radiative cooling below the ambient temperature is experimentally demonstrated, while showing whitish color under sunlight. The cooling device consists of a poly(methyl methacrylate) layer with randomly distributed silica nanoshells and a polydimethylsiloxane (PDMS) layer on an Ag mirror. The non-resonant nanoshells exhibit uniform diffuse reflection over the solar spectrum, while fully transparent for a selective thermal radiation from the underneath PDMS layer. In the temperature measurement under the sunlight irradiation, the device shows 2.3 degrees C cooler than the ambient, which is comparable to or even better than the conventional device without the nanoshells. Our approach provides a simple yet powerful nanophotonic structure for realizing a scalable and practical daytime radiative cooling device without a glaring reflective surface. No potential conflict of interest relevant to this article was reported.

Japan Society of Applied Physics Acta Medica Okayama 0021-4922 59 SK 2020 Design of non-circular membranes metasurfaces for broadband sound absorption SKKA06 EN Keita Watanabe Okayama University Mikiya Fujita Okayama University Kenji Tsuruta Okayama University Acoustic metasurfaces have been attracting much attention due to their effectiveness in controlling sound wave propagation despite a structure well below the wavelength at operating frequency. We propose a novel decorated membrane resonator structure with multiple circular membranes leading to multiplexing the resonant modes through breaking symmetry of the membrane's vibrational modes. By numerical analysis, the structure is optimized for wideband (500 to 1500 Hz) sound absorption. The designed structure is fabricated by using a 3D printer and its sound absorption property is verified experimentally by an impedance tube measurement. The results demonstrate that the present approach is simple but effective to broadband sound absorption with thin and lightweight artificial acoustic structures. No potential conflict of interest relevant to this article was reported.

Nature Publishing Group Acta Medica Okayama 2041-1723 10 2019 Ultrafast isomerization-induced cooperative motions to higher molecular orientation in smectic liquid-crystalline azobenzene molecules 4159 EN Masaki Hada Graduate School of Natural Science and Technology, Okayama University Daisuke Yamaguchi Department of Chemistry & Biotechnology, School of Engineering, The University of Tokyo Tadahiko Ishikawa School of Science,Tokyo Institute of Technology Takayoshi Sawa Graduate School of Natural Science and Technology, Okayama University Kenji Tsuruta Graduate School of Natural Science and Technology, Okayama University Ken Ishikawa School of Materials and Chemical Technology, Tokyo Institute of Technology Shin-Ya Koshihara School of Science,Tokyo Institute of Technology Yasuhiko Hayashi Graduate School of Natural Science and Technology, Okayama University Takashi Kato Department of Chemistry & Biotechnology, School of Engineering, The University of Tokyo The photoisomerization of molecules is widely used to control the structure of soft matter in both natural and synthetic systems. However, the structural dynamics of the molecules during isomerization and their subsequent response are difficult to elucidate due to their complex and ultrafast nature. Herein, we describe the ultrafast formation of higherorientation of liquid-crystalline (LC) azobenzene molecules via linearly polarized ultraviolet light (UV) using ultrafast time-resolved electron diffraction. The ultrafast orientation is caused by the trans-to-cis isomerization of the azobenzene molecules. Our observations are consistent with simplified molecular dynamics calculations that revealed that the molecules are aligned with the laser polarization axis by their cooperative motion after photoisomerization. This insight advances the fundamental chemistry of photoresponsive molecules in soft matter as well as their ultrafast photomechanical applications. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 36 1 2001 Structure and Cohesive Energy of Large Spherical Coulomb Clusters 41 49 EN Hiroo Totsuji Tokunari Kishimoto Chieko Totsuji Kenji Tsuruta 10.18926/46999 The ground state of spherical clusters of charged particles of one species confined by the three-dimensional parabolic potential is investigated by molecular dynamics simulations with the system size from N = 5000 to N = 1.2 × 10(5) . The cohesive energy per particle is compared between the shell-structured clusters and spherical finite bcc lattices with relaxed surfaces, the former and the latter being the ground states for small systems and for the large enough systems, respectively. It is shown that, when N > N(c)(N(c) > N), finite bcc lattices with relaxed surfaces (the shell structures) have stronger cohesion than the shell structures (finite bcc lattices with relaxed surfaces) and the critical value of the transition N(c) is estimated to be 10(4) < N(c) < 1.4 × 10(4) . The nucleation of the bcc lattice in the shell-structured cluster of 2 × 10(4) ions is observed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 37 1 2002 Estimation of the screening length and the electric charge on particles in single-layered dusty plasma crystals 11 14 EN Chieko Totsuji Muhammad S. Limant Kenji Tsuruta Hiroo Totsuji 10.18926/46968 A theoretical approach which has been successful in reproducing results of molecular-dynamics simulations on dusty plasmas is applied to estimate the screening length and the electric charge of two-dimensional dust crystals of melamine particles in the discharge chamber experiment. It has been found that the screening length is of the same order of magnitude as the inter-particle distance and the electric charge decreases on increasing number density of dust particles. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 38 1-2 2004 Dynamical Properties of Two-Dimensional Yukawa Liquids: A Molecular Dynamics Study 33 37 EN M. Sanusi Liman Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/46950 The dynamic structure factor and the spectrum of the momentum-density fluctuations of 2D Yukawa liquids are analyzed in the domain of weak and intermediate coupling and screenlng parameters. The dispersion relations of the longitudinal and transverse collective excitations are obtained and compared with the random phase approximation (RPA) and harmonic approximation for triangular lattice. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 38 1-2 2004 Structure of Dusty Plasma under Microgravity 29 32 EN Hiroo Totsuji Chieko Totsuji Takafumi Ogawa Kenji Tsuruta 10.18926/46949 The structure of dust particles in dusty plasmas under microgravity has been analyzed by molecular dynamics simulation. The charge neutrality condition satisfied by the system composed of dust particles and ambient plasma is properly taken into account. It is shown that dust particles form shell structures at low temperatures and the number of shells are obtained as a phase diagram in the plane of two parameters characterizing the system: the number of particles and the strength of screening. It is also shown that these structures are almost independent of the strength of screening. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 70 1 2004 Thermodynamics of a two-dimensional Yukawa fluid EN Hiroo Totsuji M. Sanusi Liman Chieko Totsuji Kenji Tsuruta Thermodynamic quantities of a two-dimensional Yukawa system, a model for various systems including single-layered dust particles observed in dusty plasmas, are obtained and expressed by simple interpolation formulas. In the domain of weak coupling, the analytical method based on the cluster expansion is applied and, in the domain of intermediate and strong coupling, numerical simulations are performed. Due to reduced dimensionality, the treatment based on the mean field fails at the short range and exact behavior of the binary correlation is to be taken into account even in the case of weak coupling. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 72 3 2005 Structure of spherical Yukawa clusters: A model for dust particles in dusty plasmas in an isotropic environment EN Hiroo Totsuji Takafumi Ogawa Chieko Totsuji Kenji Tsuruta The structure of spherical clusters composed of Yukawa particles is analyzed by molecular dynamics simulations and theoretical approaches as a model for dust particles in dusty plasmas in the isotropic environment. The latter condition is expected to be realized under microgravity or by active cancellation of the effect of gravity on the ground. It is found that, at low temperatures, Yukawa particles form spherical shells and, when scaled by the mean distance, the structure is almost independent of the strength of screening including the case of the Coulomb interaction. The positions and populations of shells and the conditions for the change of the number of shells are expressed by simple interpolation formulas. Shells have an approximately equal spacing close to that of triangular lattice planes in the bulk close-packed structures. It is shown that, when the cohesive energy in each shell is properly taken into account, the shell model reproduces the structure of spherical Yukawa clusters to a good accuracy. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 71 4 2005 Ordering of dust particles in dusty plasmas under microgravity EN Hiroo Totsuji Chieko Totsuji Takafumi Ogawa Kenji Tsuruta Structure formation of dust particles in dusty plasmas under microgravity has been simulated by the molecular dynamics method. It is shown that, at low temperatures, dust particles are organized into layered spherical shells. The number of shells is a function of the system size and the strength of screening by ambient plasma particles, while the dependency on the latter is much weaker. In the simulation, the condition of the charge neutrality satisfied by the system of dust particles and plasma particles is properly taken into account. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 44 2010 Numerical Simulation of Acoustic Waves in a Two-Dimensional Phononic Crystal: Negative Refraction 7 12 EN Kenji Tsuruta 10.18926/19954 The lens effect of acoustic waves in a two-dimensional (2D) phononic crystal is studied by numerical simulation based on the finite-difference time-domain (FDTD) method. We calculate the phonon band structure of 2D phononic crystals, consisting of metal cylinders placed periodically in water. Lens effect is observed by the negative refraction of acoustic waves, which results in refocusing of the waves at the point outside the crystal. To increase the focal intensity, we introduce a 2D phononic crystal shield with a different composition of material, which returns the incident waves back to the lens via the perfect reflection. Also, the dependence on filling fraction of metal in the crystal is studied. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 44 2010 FDTD Analysis on Optical Connement Structurewith Electromagnetic Metamaterial 1 6 EN Kenji Tsuruta 10.18926/19953 In this paper, we investigate a light-confinement phenomenon in the structure which has triangular latice composed of Double NeGative Metamaterial (DNGM). In geometrical optics consideration, this structure is expected to confine lights completely by sequential refractions in the structure. We demonstrate it by using the two dimensional finite-difference time-domain simulations. We introduce Drude-Lorentz model for dielectric and magnetic dispersion of the material at optical frequencies. We analyze quantitatively the effects of energy loss in the DNGM on the light-confinement efficiency. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 O(N) Tight-Binding Algorithm for Large-Scale Molecular Dynamics Simulations 71 77 EN Kenji Tsuruta Hiroo Totsuji Chieko Totsuji 10.18926/19674 A parallel tight-binding molecular dynamics with an order-N [O(N))] algorithm is implemented to perform large-scale simulation of nanostructured materials. The algorithm is based on the Fermi-operator expansion of an electronic energy and force, and we present its basic formalisms. Accuracy necessary for molecular-dynamics simulations can be obtained by a proper truncation in the expansion. Parallel efficiency on a parallel PC cluster shows nearly ideal scaling behavior with respect to the number of processors. Applicability of the method to a silicon-carbide system is examined. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 Multicomponent Plasmas in Penning-Malmberg Traps 61 69 EN Hiroo Totsuji Kenji Tsuruta Chieko Totsuji 10.18926/19673 The behavior of multicomponent plasmas in the Penning-Malmberg traps is discussed with the parameters corresponding to experiments with antiprotons and cryogenic electrons. The relaxation times for the energy transfer antiprotons to electrons and between parallel and perpendicular components of electrons are estimated. It is shown that, depending on the values of parameters, both the former and the latter can be the bottleneck in the cooling process. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 Density Functional Molecular Dynamics of Hydrogen Plasma 51 59 EN Hiroo Totsuji Kenji Tsuruta Chieko Totsuji 10.18926/19671 Density functional molecular dynamics method is applied to hydrogen plasma in the domain of liquid metallic hydrogen. Tentative results for the proton-proton pair distribution function and the electron-proton pair distribution function are obtained. It is shown that with the increase of the parameter γ(s), we have increasingly strong screening of proton charge by electrons and the decrease of electron density in the domain between protons. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 43 2009 Information Transfer and Entanglement Creation by Spin Chains: Effects of Noise and Asymmetry 22 26 EN Hiroo Totsuji Chieko Totsuji Kenji Tsuruta 10.18926/17831 For the transfer of quantum information and the creation of entangled states, the application of tuned spin chains, systems of spins with the nearest-neighbor coupling tuned so as to give high efficiency, has been proposed and some examples of high performance have been given by several authors. In this article, the effect of deviations from tuned values and the effect of resultant asymmetry are investigated through numerical simulations and theoretical analyses. It is shown that there exists a system where the transfer efficiency is comparable with exactly tuned ones and, at the same time, robust to noises in the coupling constants. It is also shown that the effect of asymmetry on the efficiency of entanglement creation is of the second order when the asymmetry is small. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 43 2009 FDTD Simulations of Acoustic Waves in Two-DimensionalPhononic Crystals using Parallel Computer 16 21 EN Kenji Tsuruta Chieko Totsuji Hiroo Totsuji 10.18926/17829 The finite-difference time-domain (FDTD) method has been applied to the calculation of the phonon band structure of two-dimensional (2D) phononic crystals, consisting of metal cylinders placed periodically in liquid. By comparing several combinations of materials for metal cylinder and liquid, we analyze the dependence of the band structures on sound speed and density of liquid media. Moreover, the negative refraction of the acoustic waves is observed at the interfaces between phononic crystal slab and the liquid. We find that an acoustic“lens effect”with the slab appears due to the negative refractions. The relationship between the focal intensity in the lens effect and the band structure is discussed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 1349-6115 43 2009 Dispersion Models and Electromagnetic FDTD Analyses ofNanostructured Metamaterials using Parallel Computer 8 15 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/17826 Metamaterial which has negative permittivity and permeability is investigated via computer simulations. Effects of the nanostructure on dielectric and magnetic properties of the material are taken into account by introducing the Drude-Lorentz model in the materials dispersion. We include multi-band process in the dielectric response in order to reproduce accurately experimental values of bulk Au thin film. Size effect on the dispersion is examined by comparing the model with that of a noble metal particle. Based on the dispersion model constructed, we analyze the electromagnetic response of nanostructured metamaterials to evanescent waves at microwave and optical frequencies via finite-difference time-domain simulatioins on parallel computer. A re- focusing and an amplification of the evanescent waves propagating through a metamaterial, consisting of metal slab/vacuum stacking, is demonstrated for the frequencies of 30GHz and 744THz. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 35 1-2 2001 Molecular Dynamics of Yukawa System using the Fast Multipole Method 77 95 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/15361 In order to perform the large-scale molecular dynamics simulation of the Yukawa system, a mathematical expression for molecular dynamics using the fast multipole method is described. The model simulations are also performed to test the performance of our implementation of the FMM. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 35 1-2 2001 Nonorthogonal Tight-Binding Molecular Dynamics for Si(1-x)Ge(x) Alloys 63 75 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/15358 We present a theoretical study of Si(1-x)Ge(x) alloys based on tight-binding molecular dynamics (TBMD) calculations. First, we introduce a new set of nonorthogonal tight-binding parameters for silicon and germanium based on the previous work by Menon and Subbaswamy [Phys. Rev. B 55, 9231 (1997); J. Phys: Condens. Matter 10, 10991 (1998)]. We then apply the method to structural analyses of Si(1-x)Ge(x) alloys. The equilibrium volume and atomic structure for a given x are obtained by the TBMD method. We also calculate the bulk modulus B, elastic constants C(11), C(12) and C(44) as a function of x. The results show that the moduli vary monotonically, but nonlinearly, between the values of Si crystal and Ge crystal. The validity of the results is also discussed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 39 1 2005 Large-Scale Molecular Dynamics Simulation of CoulombClusters: A Finite-Temperature Analysis 52 55 EN Katsuya Kanamori Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14152 Thermal behavior of Coulomb clusters in a three dimensional confining potential is investigated by molecular dynamics simulations for system sizes of 1,000 to 20,288 ions. The specific heat of the system of shell-structured 20,000 ions is peaked almost at the same temperature as the system of bcc-structured 20,288 ions with much sharper structure for the latter. The diffusion coefficient and the peak to valley ratio of the two-dimensional pair distribution function on the outermost shell are obtained both as a function of temperature. The rotational movement of each shell in the system of 104 ions is observed. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 39 1 2005 Electron Dynamics in Semiconducting Nanowires: A Real-Space,Polynomial-Expansion Approach 46 51 EN Keisuke Kadono Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14150 We present a real-space, polynomial-expansion approach to electron dynamics in nanostructured semiconductors. The Chebyshev expansion method is employed for efficient calculation of timeevolution of single-electron wave function. Details of the formulation are described. The method is applied to the electron transport in nanostructured semiconductors such as Si nanowires. The mean-square displacement and diffusivity of electron in Si chains are obtained as functions of length of the chains. The results show clearly ballistic behavior of electron in the pure Si chain. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 40 1 2006 Distribution of Electrons in Quantum Dots Analyzed by Classical Mapping and Molecular Dynamics 40 43 EN Miyake Takashi Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14121 The electron system of arbitrary degeneracy can be mapped onto a classical system where electrons of the same spin are assigned an additional interaction and the effect of degeneracy is taken into account through an imaginative temperature. We apply this method to electrons in quantum dots modeled as two-dimensional electron liquid confined in a finite domain by a harmonic potential. We analyze distribution functions by molecular dynamics instead of solving integral equations which are not so useful in the case without translational invariance. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 40 1 2006 Stochastic-Dierence-Equation Method for Long Time-scaleMolecular Dynamics Simulations 36 39 EN Atsushi Uchida Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14120 We present a Stochastic-Difference-Equation (SDE) approach to long time-scale molecular dynamics (MD) simulations, which are required for nanosecond-scale phenomena. In this method, the MD trajectory in a fixed time period is obtained as a stationary solution of an action functional based on an error accumulation of the equation of motion along the path, thus reducing the problem to a boundary-value problem, instead of an initial-value problem in the ordinary MD method. We apply the method to formation processes of Cu thin film via nanocluster deposition onto a substrate. The applicability of the SDE algorithm to the problem and the effects of the choice of SDE parameters on the optimization processes of configuration pathway are examined. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 40 1 2006 Melting of Spherical Yukawa Clusters Analyzed by Monte CarloSimulation 31 35 EN Takafumi Ogawa Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14119 We analyze the melting of spherical Yukawa clusters by Monte Carlo simulations. Spherical clusters are expected to be found in dusty plasmas in an isotropic environment such as microgravity and serve as a model for classical clusters. We obtain the specific heat through fluctuations of the potential energy and identify its peak as the transition temperature. Melting temperatures are compared with those of bulk Yukawa systems and it is confirmed that the melting temperature increases and approaches the bulk value with the increase of the system size. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 42 1 2008 Spin Polarization of Two-Dimensional Electron System in a Finite Domain 56 59 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14061 We analyze the ground state of the two-dimensional quantum system of electrons confined in a parabolic potential with the system size around 100. We map the system onto a classical system on the basis of the classical-map hypernetted-chain (CHNC) method which has been proven to work in the integral-equation-based analyses of uniform unbounded systems and then apply classical numerical simulations. We find that the confined system undergoes the transition to the spin polarized state with the decrease of the average density and the corresponding critical value is as low as rs ∼ 0.3 in terms of the usual rs parameter estimated for the average density. As the ground state for given value of the rs parameter, our data give the critical value for the transition around 20 which is consistent with the known possibility. The advantage of our method is a direct applicability to geometrically complex systems which are difficult to analyze by integral equations. The application to the structure like quantum dots reported here is the first example of such applications. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 42 1 2008 Numerical Simulations of Two-dimensional Electron Fluid : An Application of Classical-map Hypernetted-chain Method 48 52 EN Chieko Totsuji Kenji Tsuruta Hiroo Totsuji 10.18926/14059 Based on the mapping introduced by the classical-map hypernetted-chain (CHNC) method, classical numerical simulations, Monte Carlo and molecular dynamics, have been applied to the twodimensional electron fluid and the results are compared with those of quantum Monte Carlo simulations hitherto reported. It is shown that polarization properties of the ground state obtained by the diffusion Monte Carlo method are reproduced within the accuracy of quantum simulations by both of two mapping functions for the quantum temperature which have been proposed within the CHNC method. These results may serve as the basis of numerical simulations based on the CHNC method which are applicable to finite non-periodic systems like quantum dots and systems at finite temperatures. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 42 1 2008 Vibrational Properties of Si Crystal with Vacancy : A Tight-Binding Study 44 47 EN Kenji Tsuruta Chieko Totsuji Hiroo Totsuji 10.18926/14058 To analyze vibrational properties of Si crystal with a single charge-neutral vacancy, we perform large-scale simulations based on tight-binding molecular-dynamics method. Vibrational modes and frequencies are obtained by diagonalizing dynamical matrix within a harmonic approximation. Results indicate that there exist vibrational modes spatially localized around the vacancy and large frequency shifts associated with the localized modes contribute significantly to reduction of the vibrational free energy. No potential conflict of interest relevant to this article was reported.