Faculty Profiles - TSURUTA Kenji

Papers - TSURUTA Kenji

Division display 81 - 100 of about 148 ／ All the affair displays >>

Initial Stage of Consolidation of Silicon-Carbide Nanocrystals under Pressure: A Tight-Binding Molecular-Dynamics Study Reviewed

Kenji Tsuruta

JOURNAL OF NANOMATERIALS 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：HINDAWI PUBLISHING CORPORATION

Tight-binding molecular-dynamics (TBMDs) simulations are performed to study atomic and electronic structures during high-temperature consolidation processes of nanocrystalline silicon carbide under external pressure. We employ a linear-scaling method (the Fermi-operator expansion method) with a scalable parallel algorithm for efficient calculations of the long time-scale phenomena. The results show that microscopic processes of the consolidation depend strongly on initial orientations of the nanocrystals. It is observed that an orientational rearrangement of the nanocrystals initially misaligned is induced by an instantaneous shearing force between nanocrystals, whereas the aligned system undergoes densification without shearing. Analysis on an effective-charge distribution and an average bond-order distribution reveals electronic-structure evolutions during these processes.

DOI： 10.1155/2011/308495

Molecular Dynamics Study on Dielectric Properties of Silicon Oxynitride: Composition and Microstructure Dependence Reviewed

Munemasa Tomita, Kenji Tsuruta

ELECTROCERAMICS IN JAPAN XIV 485 287 - 290 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

Extra-long molecular-dynamics simulations are performed to study the interplay between dielectric properties and microstructures of silicon oxynitride. We quantitatively obtained the ionic permittivity and its linear dependence on nitrogen concentration. Analyses on microstructure of the oxynitride show that, as the N concentration increases, N atoms enter Si-O networks creating smaller-sized rings. While overall tendency of dielectric constant is monotonic increase on the N concentration, microscopic characteristics, such as local displacement of atoms, are strongly depend on local bonding environments.

DOI： 10.4028/www.scientific.net/KEM.485.287

Acoustic lens using sonic crystal for energy-transmission application Reviewed

Y. Kanno, Y. Kasai, K. Tsuruta, K. Fujimori, H. Fukano, S. Nogi

2011 IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and Applications, IMWS-IWPT 2011 - Proceedings 207 - 210 2011

Language：English Publishing type：Research paper (international conference proceedings)

We design and characterize a two-dimensional sonic crystal (SC) to manipulate the propagation of acoustic waves by numerical simulation based on the finite-difference time-domain (FDTD) method and by ultrasonic measurement. Two types of SC for an acoustic lens effect are studied. One is a homogeneous periodic structure exhibiting negative refraction, and the other has a hetero-structure. Negative refraction behavior in the simulation is good agreement with the experiment in the frequency range around 1.2MHz. We also observe a lens effect for far-field wave in the hetero-structured SC. These results indicate that a novel energy-transmission/harvesting device can be designed using SCs. © 2011 IEEE.

DOI： 10.1109/IMWS.2011.5877131

Density-Functional Analysis on Vacancy Orbital and its Elastic Response of Silicon Reviewed

Takafumi Ogawa, Kenji Tsuruta, Hiroshi Iyetomi, Hiroshi Y. Kaneta, Terutaka Goto

RELIABILITY AND MATERIALS ISSUES OF SEMICONDUCTOR OPTICAL AND ELECTRICAL DEVICES AND MATERIALS 1195 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOC

Recent experiments on ultrasonic measurements of non-doped and boron-doped silicon indicate that vacancies in crystalline silicon can be detected through the elastic softening at low temperature. This is attributed to enhanced response of electronic quadrupole localized at the vacancies to the elastic strain. In the present work, the electronic quadrupole moment of the vacancy orbital in silicon and their strain susceptibility are evaluated quantitatively by using the density-functional method. We show the orbital of gap state is localized around vacancy but extended over several neighbors. The effect of applied magnetic field on the vacancy orbital and its multipole structures are also investigated. We find that the results obtained from these calculations are consistent with the ultrasonic experiments.

DOI： 10.1557/PROC-1195-B08-11

Classical and Hybrid Density-Functional/Classical Molecular Dynamics Study of Dislocation Core in Alumina Ceramic Reviewed

Kenji Tsuruta, Toshiyuki Koyama, Shuji Ogata

MATERIALS TRANSACTIONS 50 ( 5 ) 1015 - 1018 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

We perform molecular-dynamics simulation,, to investigate the atomic and electronic structures of a basal edge dislocation it) alpha-Al2O3. The core structure consisting of two non-stoichiometric partial dislocations, which has been recently proposed by an experiment, is examined by an empirical interatomic-potential model and by a hybrid quantum/classical approach. The atomic rearrangements in the full and in the partial dislocation cores are analyzed. The local electronic structure in the full dislocation core is evaluated by the density-functional method applied for a quantum-cluster region in the hybrid simulations. Interaction potentials between partial dislocations are investigated by the classical model. Results preliminarily obtained show that the partials aligned normal to a basal plane ({10001}) has a short-ranged repulsive nature approximately within 8 angstrom. [doi: 10.2320/matertrans.MC200833]

DOI： 10.2320/matertrans.MC200833

An FDTD Analysis of Nanostructured Electromagnetic Metamaterials Using Parallel Computer Reviewed

Ryosuke Umeda, Chieko Totsuji, Kenji Tsuruta, Hiroo Totsuji

MATERIALS TRANSACTIONS 50 ( 5 ) 994 - 998 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

Metamaterial with negative permittivity and permeability is studied by means of computer simulations. We analyze the electromagnetic response of nanostructured metamaterials to evanescent waves at optical frequency via the finite-difference time-domain simulations on parallel computer. Effects of the nanostructure on dielectric and magnetic properties are taken into account by introducing the Drude-Lorentz model in the materials dispersion. Size effect on the dispersion is examined by comparing the model with that of a noble metal particle. A re-focusing and an amplification of the evanescent waves propagating through a metamaterial, consisting of metal slabs/vacuum stacking, are demonstrated for the frequency range at 614-744 THz. By properly treating the materials dispersion, we show that the nanostructured metamaterial may behave as a left-handed material in the optical range. [doi:10.2320/matertrans.MC200822]

DOI： 10.2320/matertrans.MC200822

Negative Refraction of Acoustic Waves in a Two-Dimensional Phononic Crystal via FDTD Simulation Reviewed

Tomoyuki Kurose, Kenji Tsuruta, Chieko Totsuji, Hiroo Totsuji

MATERIALS TRANSACTIONS 50 ( 5 ) 1004 - 1007 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

Negative refraction 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 a 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. The negative refraction of the acoustic waves is observed at the interfaces between the 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 of the phononic crystal is quantitatively discussed. [doi: 10.2320/matertrans.MC200823]

DOI： 10.2320/matertrans.MC200823

A classical-map simulation of two-dimensional electron fluid: an extension of classical-map hypernetted-chain theory beyond the hypernetted-chain approximation Reviewed

Chieko Totsuji, Takashi Miyake, Kenta Nakanishi, Kenji Tsuruta, Hiroo Totsuji

JOURNAL OF PHYSICS-CONDENSED MATTER 21 ( 4 ) 2009.1

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

A method for numerically simulating quantum systems is proposed and applied to the two-dimensional electron fluid at T = 0. This method maps quantum systems onto classical ones in the spirit of the classical-map hypernetted-chain theory and performs simulations on the latter. The results of the simulations are free from the assumption of the hypernetted-chain approximation and the neglect of the bridge diagrams. A merit of this method is the applicability to systems with geometrical complexity and finite sizes including the cases at finite temperatures. Monte Carlo and molecular dynamics simulations are performed corresponding to two previous proposals for the 'quantum' temperature and an improvement in the description of the diffraction effect. It is shown that one of these two proposals with the improved diffraction effect gives significantly better agreement with quantum Monte Carlo results reported previously for the range of 5 <= r(s) <= 40. These results may serve as the basis for the application of this method to finite non-periodic systems like quantum dots and systems at finite temperatures.

DOI： 10.1088/0953-8984/21/4/045502

Spin polarization of two-dimensional electron system in parabolic potential Reviewed

Takashi Miyake, Chieko Totsuji, Kenta Nakanishi, Kenji Tsuruta, Hiroo Totsuji

PHYSICS LETTERS A 372 ( 40 ) 6197 - 6201 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We analyze the ground state of the two-dimensional quantum system of electrons confined in a parabolic potential with the system size around 100 at 0 K. 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 systems and apply classical Monte Carlo and molecular dynamics simulations. We find that, when we decrease the strength of confinement keeping the number of confined electrons fixed, the energy of the spin-polarized state with somewhat lower average density becomes smaller than that of the spin-unpolarized state with somewhat higher average density. This system thus undergoes the transition from the spin-unpolarized state to the spin polarized state and the corresponding critical value of r(s) estimated from the average density is as low as r(s) similar to 0.4 which is much smaller than the r(s) value for the Wigner lattice formation. When we compare the energies of spin-unpolarized and spin-polarized states for given average density, our data give the critical r(s) value for the transition between unpolarized and polarized states around 10 which is close to but still smaller than the known possibility of polarization at r(s) similar to 27. The advantage of our method is a direct applicability to geometrically complex systems which are difficult to analyze by integral equations and this is an example. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physleta.2008.08.036

Vibrational Properties of Si Crystal with Vacancy: A Tight-Binding Study

Takafumi Ogawa, Kenji Tsuruta, Chieko Totsuji, Hiroo Totsuji, Hiroshi Iyetomi

Memoirs of the Faculty of Engineering, Okayama University 42 ( 1 ) 44 - 47 2008.1

Nickel-related defect in diamond: A tight-binding molecular-dynamics study Reviewed

Kenji Tsuruta, Satoshi Emoto, Chieko Totsuji, Hiroo Totsuji

COMPUTATIONAL MATERIALS SCIENCE 38 ( 4 ) 873 - 882 2007.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Structural, electronic, and magnetic properties of isolated Ni impurities at point defects and a dislocation core in diamond are investigated using tight-binding molecular-dynamics simulations. The results show the structural stabilization associated by lowering local symmetry in the cases of point defects. The segregation energies of Ni impurity for a substitutional site and for an interstitial site in the dislocation core are estimated to be in the same order within 0.2 eV. The local electronic density-of-states reveals that the gap states appeared by the insertion of Ni impurity are strongly localized around the Ni sites. Magnetic moments on neighboring C atoms are induced so as to screen the moment on the Ni atom except for the case of interstitial Ni impurity in which the total magnetic moment remains non-zero. Analyses indicate that localized atomic d states on the Ni atom and the p-d coupling between Ni and neighboring C atoms are responsible for the residual magnetic moment in the system with an interstitial Ni defect. In the other systems investigated, on the other hand, the bonding states between Ni impurity and its neighboring C atoms are dominated by the s-p coupling. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.commatsci.2006.06.003

Two-step melting of spherical Yukawa and Coulomb clusters Reviewed

Takafumi Ogawa, Hiroo Totsuji, Chieko Totsuji, Kenji Tsuruta

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 12 ) 2006.12

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

By extensive Monte Carlo simulations, two separate peaks are found in the specific heat of relatively small spherical clusters of particles with 100 < N < 400, interacting via the Yukawa and Coulomb potentials and confined in the external field. The analyses of the diffusion and positional fluctuations show that these peaks at lower and higher temperatures reflect the loss of intrashell two-dimensional ordering and of the radial ordering, respectively. The magnitudes of the fluctuations in the outermost shell are consistent with the conventional Lindemann criterion. The results can be verified by experiments in ion traps and in dusty plasmas under microgravity or equivalent isotropic environments.

DOI： 10.1143/JPSJ.75.123501

Structure of spherical Yukawa clusters Reviewed

Hiroo Totsuji, Takafumi Ogawa, Chieko Totsuji, Kenji Tsuruta

Journal of Physics A: Mathematical and General 39 ( 17 ) 4545 2006.4

Dynamics of melting of spherical Yukawa and Coulomb clusters Reviewed

Takafumi Ogawa, Hiroo Totsuji, Chieko Totsuji, Kenji Tsuruta

NON-NEUTRAL PLASMA PHYSICS VI 862 242 - 247 2006

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

Spherical Yukawa and Coulomb clusters are composed of charged particles interacting via the Yukawa and Coulomb potential and confined by the external potential. Melting transitions of these clusters are analyzed by Monte Carlo (MC) and molecular dynamics (MD) simulations. By MC simulations, it is found that the specific heat of relatively small clusters (100 <= N <= 400) has two peaks. The diffusion analyses by MC and MD simulations and the fluctuation analyses related to the Lindemann criteria indicate that two peaks at lower and higher temperatures reflect the losses in ordering in azimuthal and radial directions, respectively.

DOI： 10.1063/1.2387929

Structure and thermodynamics of spherical Yukawa and Coulomb clusters Reviewed

Hiroo Totsuji, Takafumi Ogawa, Chieko Totsuji, Kenji Tsuruta

NON-NEUTRAL PLASMA PHYSICS VI 862 232 - 241 2006

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

Structures in the ground state and thermodynamics related to melting of spherical Yukawa and Coulomb clusters confined in external fields of less than 103 particles are discussed on the basis of molecular dynamics and Monte Carlo simulations and theoretical methods. At low temperatures, particles form concentric shell structures which are expressed by simple formulas and insensitive to the strength of screening. Structures are reproduced by the shell model when the intrashell cohesive energy is properly taken into account. The specific heat of clusters of relatively small sizes 100 <= N-d <= 400 has two peaks as a function of temperature. By analyses of diffusions, it is shown that the peaks at lower and higher temparatures corresponds to the loss of ordering in the azimuthal and radial (and therefore total) ordering, respectively. Magnitudes of fluctuations in the outermost shell are consistent with the conventional Lindemann criterion.

DOI： 10.1063/1.2387928

Structure of finite two-dimensional systems of dust particles at finite temperatures Reviewed

H Totsuji, C Totsuji, MS Liman, K Tsuruta

PHYSICS OF PLASMAS 12 ( 10 ) 2005.10

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

The structure of confined two-dimensional systems of dust particles in dusty plasmas is analyzed at finite temperatures by numerical simulations and theoretical approaches. The finite Yukawa system is adopted as a model for these systems and the variational method which has been successful in reproducing structures at low temperatures is extended to finite temperatures through replacement of the cohesive energy by the Helmholtz free energy recently given in the form of simple interpolation formulas. The results are compared with those of numerical simulations and their satisfactory agreement has been obtained. Finite-temperature structures presented here will be useful to evaluate the physical parameters of the two-dimensional systems of dust particles often formed near the boundary between the plasma bulk and the sheath.

DOI： 10.1063/1.2116827

Structure of spherical Yukawa clusters: A model for dust particles in dusty plasmas in an isotropic environment Reviewed

Hiroo Totsuji, Takafumi Ogawa, Chieko Totsuji, Kenji Tsuruta

Physical Review E 72 ( 3 ) 036406 2005.9

Ordering of dust particles in dusty plasmas under microgravity Reviewed

Hiroo Totsuji, Chieko Totsuji, Takafumi Ogawa, Kenji Tsuruta

Physical Review E 71 ( 4 ) 045401 2005.4

Thermodynamics of a two-dimensional Yukawa fluid Reviewed

H Totsuji, MS Liman, C Totsuji, K Tsuruta

PHYSICAL REVIEW E 70 ( 1 ) 2004.7

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

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.

DOI： 10.1103/PhysRevE.70.016405

Thermodynamics of a two-dimensional Yukawa fluid Reviewed

Hiroo Totsuji, M. Sanusi Liman, Chieko Totsuji, Kenji Tsuruta

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 70 ( 1 ) 7 2004

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

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. © 2004 The American Physical Society.

DOI： 10.1103/PhysRevE.70.016405

　 PREV - NEXT 　

1
2
3
4
5
6
7
8