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Sasa, Narimasa; Kano, Takuma*; Machida, Masahiko; L'vov, V. S.*; Rudenko, O.*; Tsubota, Makoto*
Physical Review B, 84(5), p.054525_1 - 054525_6, 2011/08
Times Cited Count：46 Percentile：84.35(Materials Science, Multidisciplinary)In a 2048
simulation of quantum turbulence within the Gross-Pitaevskii equation, it is demonstrated that the large-scale motions have a classical Kolmogorov-1941 energy spectrum 
, followed by an energy accumulation with 
const at about the reciprocal mean intervortex distance. This behavior was predicted by the L'vov-Nazarenko-Rudenko bottleneck model of gradual eddy-wave crossover, further developed in the paper.
dinger equation on 
gridsImamura, Toshiyuki*; Kano, Takuma*; Yamada, Susumu; Okumura, Masahiko*; Machida, Masahiko
International Journal of High Performance Computing Applications, 24(3), p.319 - 334, 2010/08
Times Cited Count：0 Percentile：0.02(Computer Science, Hardware & Architecture)In order to explore quantum dynamics of coupled Josephson junctions, we develop a program solving directly the time-dependent Schrdinger equation by diagonalizing the Hamiltonian matrix and obtaining its ground and multiple low-lying excitation states. The Schrdinger equation is defined on 
grids, in which 
is the number of grid points discretized on a characteristic phase space of each junction and 
is the number of coupled junctions. In this paper, the calculated maximum system is that 
and 
, i.e. the number of degrees of freedom reaches (=4,294,967,296). We examine possible effective numerical schemes and make a parallel tuning to optimize the communication on the Earth Simulator. We sustain floating-point operation performance exceeding 20% of the peak on 512 nodes (4,096 PEs). From systematic calculations, we find a new concept that "quantum-assisted synchronization" occurs with downsizing the junction plane. This is a discovery adding a quantum flavor to the classical concept "synchronization".
Yamada, Susumu; Machida, Masahiko; Kano, Takuma; Imamura, Toshiyuki*; Koyama, Tomio*
Journal of Physics and Chemistry of Solids, 69(12), p.3395 - 3397, 2008/12
Times Cited Count：0 Percentile：0(Chemistry, Multidisciplinary)We numerically investigate a dependence of pairing interaction strength on quantum coherence and related tunneling dynamics in order to clarify whether the strong pairing interaction suppresses quantum coherent characters. The simulation is performed by using the attractive Hubbard model with double well potential. The simulation result reveals that the tunneling dynamics between the separated wells is dramatically suppressed with increasing the pairing interaction. This fact implies that the pair coherence is easily lost under randomness when the pairing interaction becomes very strong. We claim that such an issue is related to the loss of the pair coherence in under-doped High-
superconductors. In addition, we note that the tunneling dynamics can be directly confirmed by using the crossover from BCS to BEC in atomic Fermi gases.
Takase, Kazuyuki; Yoshida, Hiroyuki; Kano, Takuma
Annual Report of the Earth Simulator Center April 2007 - March 2008, p.217 - 221, 2008/09
no abstracts in English
five-dimensional Vlasov simulationIdomura, Yasuhiro; Ida, Masato; Kano, Takuma; Aiba, Nobuyuki; Tokuda, Shinji
Computer Physics Communications, 179(6), p.391 - 403, 2008/09
Times Cited Count：82 Percentile：95.34(Computer Science, Interdisciplinary Applications)A new conservative global gyrokinetic toroidal full- five-dimensional Vlasov simulation (GT5D) is developed using a novel non-dissipative conservative finite difference scheme. The scheme guarantees numerical stability by satisfying relevant first principles in the modern gyrokinetic theory, and enables robust and accurate simulations of tokamak micro-turbulence. GT5D is verified through comparisons of zonal flow damping tests, linear analyses of ion temperature gradient driven (ITG) modes, and nonlinear ITG turbulence simulations against a global gyrokinetic toroidal 
particle code. In the comparison, global solutions of the ITG turbulence are identified quantitatively by using two gyrokinetic codes based on particle and mesh approaches.
thin film detector for neutronsIshida, Takekazu*; Nishikawa, Masatoshi*; Fujita, Yoshifumi*; Okayasu, Satoru; Katagiri, Masaki*; Sato, Kazuo*; Yotsuya, Tsutomu*; Shimakage, Hisashi*; Miki, Shigehito*; Wang, Z.*; et al.
Journal of Low Temperature Physics, 151(3-4), p.1074 - 1079, 2008/05
Times Cited Count：36 Percentile：78.05(Physics, Applied)The superconducting neutron detector using high-quality 
B-enriched MgB thin films at higher operating temperatures has been proposed, where a resistance change induced by the nuclear reaction of neutron and B in MgB is used to detect a neutron. Cold neutrons from a nuclear research reactor irradiated the MgB detector, and the output voltage was clearly observed through a low-noise amplifier by using a digital oscilloscope. The out-of-equilibrium thermodynamics was investigated by means of the time-dependent Ginzburg-Landau equations by using the Earth Simulator.
neutron detectorsMachida, Masahiko; Kano, Takuma*; Koyama, Tomio*; Kato, Masaru*; Ishida, Takekazu*
Journal of Low Temperature Physics, 151(1), p.58 - 63, 2008/04
Times Cited Count：11 Percentile：46.07(Physics, Applied)We perform large-scale numerical simulations on the non-equilibrium superconducting dynamics after a neutron capture at the superconducting transition edge in MgB by solving the time-dependent Ginzburg-Landau equation coupled with the Maxwell and the heat diffusion equations. The simulations are carried out under the current-biased condition in order to explain experimental results made in the JAEA reactor JRR-3, and the time scale of the obtained voltage signal is found tobe almost consistent with the experiments. Moreover, the time evolution of the voltage signal is connected with that of the spatial profile of the superconducting order parameter.
Machida, Masahiko; Kano, Takuma*; Yamada, Susumu; Okumura, Masahiko; Imamura, Toshiyuki*; Koyama, Tomio*
Physica C, 468(7-10), p.689 - 694, 2008/04
Times Cited Count：18 Percentile：59.93(Physics, Applied)no abstracts in English
Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Kano, Takuma; Merzari, E.*; Ninokata, Hisashi*
Annual Report of the Earth Simulator Center April 2006 - March 2007, p.223 - 228, 2007/09
no abstracts in English
Ishida, Hisashi; Yura, Kei; Kano, Takuma; Matsumoto, Atsushi
Annual Report of the Earth Simulator Center April 2006 - March 2007, p.257 - 263, 2007/09
The Earth Simulator has the highest power ever achieved to perform molecular dynamics simulation of large-scale supra-molecular systems. We are developing a molecular dynamics simulation system, called SCUBA, which is designed to run a system composed of more than a million particles efficiently on parallel computers. This fisical year, the arrays used in the program of SCUBA were intensively optimized to reduce the amount of memory use. This optimization enabled SCUBA to perform molecular dynamics simulations of large-scale supra-molecular systems comprised of more than a million atoms on the Earth Simulator. Moreover, the Martyna-Klein-Tuckerman algorithm was extended to utilize the multiple time step method, which increases the time step length significantly. Then, in order to elucidate the dynamics of the 70S ribosome, molecular dynamics simulation of the 70S ribosome including its explicit solvent, a system which is composed of about two million atoms, has been performed using SCUBA. A model of a nascent polypeptide was included in the system to investigate how the nascent polypeptide passes through the exit tunnel within the large subunit of the 70S ribosome. The ratchet-like motion of the 70S ribosome, which is thought to be important for the genetic translation, was successfully observed.
Shimizu, Futoshi; Ogata, Shigenobu*; Kimizuka, Hajime*; Kano, Takuma; Li, J.*; Kaburaki, Hideo
Journal of the Earth Simulator, 7, p.17 - 21, 2007/06
Yamada, Susumu; Imamura, Toshiyuki*; Kano, Takuma; Ohashi, Yoji*; Matsumoto, Hideki*; Machida, Masahiko
Journal of the Earth Simulator, 7, p.23 - 35, 2007/06
In order to explore a possibility of superfluidity in confined strongly-correlated fermion systems, e.g., nano-scale cuprate High-Tc superconductors and atomic Fermi gases loaded on an optical lattice, we implement an exact diagonalization code for their mathematical model, i.e., a trapped Hubbard model on the Earth Simulator. We compare two diagonalization algorithms, the traditional Lanczos method and a new algorithm, the preconditioned conjugate gradient (PCG) method, and find that when using the PCG the total CPU time can be reduced to 1/3 
1/5 compared to the former one since the convergence can be dramatically improved by choosing a good preconditioner and the communication overhead is much more efficiently concealed in the PCG method. Consequently, such a performance improvement enables us to do systematic studies for several parameters. Numerical simulation results reveal that an unconventional type of pairing specific to the confined system, which can cause superfluidity, develops under a strong repulsive interaction.
Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Kano, Takuma; Akimoto, Hajime
Annual Report of the Earth Simulator Center April 2005 - March 2006, p.261 - 265, 2007/01
no abstracts in English
Ishida, Hisashi; Higuchi, Mariko; Yonetani, Yoshiteru*; Kano, Takuma; Jochi, Yasumasa*; Kitao, Akio*; Go, Nobuhiro
Annual Report of the Earth Simulator Center April 2005 - March 2006, p.237 - 240, 2007/01
no abstracts in English
Yamada, Susumu; Imamura, Toshiyuki*; Kano, Takuma; Machida, Masahiko
Proceedings of International Conference for High Performance Computing, Networking, Storage and Analysis (SC '06) (CD-ROM), 12 Pages, 2006/11
no abstracts in English
Takase, Kazuyuki; Ose, Yasuo*; Yoshida, Hiroyuki; Kano, Takuma; Aoki, Takayuki*
Nihon Kikai Gakkai Kanto Shibu Dai-12-Ki Sogo Koenkai Koen Rombunshu, p.229 - 230, 2006/03
no abstracts in English
/SiC interfaceMiyashita, Atsumi; Yoshikawa, Masahito; Kano, Takuma; Onuma, Toshiharu*; Sakai, Takayuki*; Iwasawa, Misako*; Soneda, Naoki*
Annual Report of the Earth Simulator Center April 2004 - March 2005, p.287 - 291, 2005/12
Silicon carbide semiconductor device is expected to be used under a severe environment like the nuclear reactor and the space environment. On the semiconductor device interface, the electric charge state of the defect decides an electric characteristic. To emulate interfacial structure the 
interface structure is generated and the electronic geometry is decided by the first-principle molecular dynamics simulation with the earth simulator. The amorphous interface structure is made by medium-scale model of about 400 atoms. The heating temperature is 4000K, the heating time is 3.0ps, the speed of rapid cooling is -1000K/ps, and SiC movable layers in the interface are assumed to be 4 layers. In temperature 2200K the 
terminal was opened to make the layer more amorphous. The model has almost abrupt interface, however, some defects energy levels were still observed in the band gap. The energy levels are originated from interfacial oxygen. The localized electronic distribution of the dangling bond causes defect energy levels.
Ishida, Hisashi; Higuchi, Mariko; Yonetani, Yoshiteru*; Kano, Takuma; Jochi, Yasumasa*; Kitao, Akio*; Go, Nobuhiro
Annual Report of the Earth Simulator Center April 2004 - March 2005, p.241 - 246, 2005/12
no abstracts in English
Ose, Yasuo*; Takase, Kazuyuki; Yoshida, Hiroyuki; Kano, Takuma; Akimoto, Hajime
Dai-18-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Yoshishu (CD-ROM), 6 Pages, 2004/12
no abstracts in English
Ishida, Hisashi; Jochi, Yasumasa*; Higuchi, Mariko; Kano, Takuma; Kitao, Akio*; Go, Nobuhiro
Annual Report of the Earth Simulator Center April 2003 - March 2004, p.175 - 179, 2004/07
no abstracts in English
