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Takezawa, Hiroki*; Tuya, D.; Obara, Toru*
Nuclear Science and Engineering, 195(11), p.1236 - 1246, 2021/11
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)This study introduces new methodologies for integrating fission reactions induced by delayed neutrons into the Multi-Region Integral Kinetic (MIK) code by using a Monte Carlo neutron transport calculation. First, it was confirmed that it is feasible to solve the Integral Kinetic Model (IKM) with delayed neutrons by the forward Euler discretization method in terms of the number of time steps. This can be done with the help of the law of radioactive decay to reflect the delay in the emission of delayed neutrons in the discretized IKM. Second, a new Monte Carlo-based methodology was introduced for calculating the cumulative distribution functions of secondary fission induced by prompt and delayed neutrons. These functions are necessary for the discretized IKM. The results of preliminary verification using the Godiva reactor confirmed the applicability of the new Monte Carlo-based methodology.
Kitagaki, Toru; Hoshino, Takanori; Yano, Kimihiko; Okamura, Nobuo; Ohara, Hiroshi*; Fukasawa, Tetsuo*; Koizumi, Kenji
Journal of Nuclear Engineering and Radiation Science, 4(3), p.031011_1 - 031011_7, 2018/07
nanocubes by solvothermal synthesisYoneda, Yasuhiro; Kohara, Shinji*; Nakashima, Koichi*; Nagata, Hajime*; Wada, Satoshi*
Japanese Journal of Applied Physics, 54(10S), p.10NC01_1 - 10NC01_6, 2015/10
Times Cited Count：4 Percentile：18.5(Physics, Applied)The atomic-scale structure of KNbO nanopowder synthesized by solvothermal method has been studied using high-energy X-ray diffraction, Rietveld refinement, and the atomic pair-distribution function (PDF) technique. It was found that the local structure of KNbO nanoparticles deviates from the average structure. The local structure was found to be rhombohedral structure though the average structure was tetragonal structure. The rhombohedral distortion of NbO
octahedra was maintained in the annealed sample.
modulated by Mn substitutionYoneda, Yasuhiro; Kohara, Shinji*; Noguchi, Yuji*; Miyayama, Masaru*
Transactions of the Materials Research Society of Japan, 40(1), p.29 - 32, 2015/03
Barium titanate (BaTiO) with a high dielectric constant is widely used in the production of ceramic capacitors. However, during sintering large numbers of ionized oxygen vacancies and conduction electrons are created. Doping with manganese is one of several ways to confine the electrons to a small region. In Mn-doped BaTiO there exist three valence states for the manganese ions, Mn
, Mn
, and Mn
. The Mn is nearly exactly incorporated into Ti sites and participates in the collective motion in the lattice. We performed local structure analysis by using atomic pair-distribution function (PDF) and X-ray absorption fine structure (XAFS). Figure 1 shows the obtained PDFs for pure BaTiO and 0.5%-Mn-doped BaTiO. All data collected at room temperature. Two obtained PDF patterns are well in agreement. Mn doping has hardly affected local structure.
TiO
( = Sr, Ba, Pb)Yoneda, Yasuhiro; Kohara, Shinji*
Ferroelectrics, 485(1), p.34 - 41, 2015/00
Times Cited Count：3 Percentile：14.61(Materials Science, Multidisciplinary)High-energy X-ray total scattering provides simultaneous information about long-range order through the Bragg peaks and short-range order through the diffuse scattering. In ferroelectric materials, short-range order structure inside the ferroelectric domains tends to deviate from the average structure. The local structure analysis is necessary to reveal the ferroelectric mechanism. We applied atomic pair-distribution function (PDF) analysis using synchrotron X-ray for the study of local structure of ferroelectrics having perovskite structure. In BaTiO, since local distortion is averaged out owing to the requirements of periodicity and harmonic lattice vibrations, the average structure showed a cubic structure. The actual structure of systems which displays so much instability and disorder can be revealed by the PDF analysis.
Yoneda, Yasuhiro; Kohara, Shinji*; Nagata, Hajime*; Fu, D.*; Takenaka, Tadashi*
Transactions of the Materials Research Society of Japan, 39(4), p.455 - 458, 2014/12
NaNbO, KNbO, and AgNbO have rhombohedral structure at low temperatures. The phase transition depends on 
-site ion with NbO octahedron. NaNbO and KNbO have structural phase transition from rhombohedral to orthorhombic with increasing temperature. On the other hand, the phase transition of AgNbO occurs from rhombohedral to monoclinic. Since the rhombohedral structure is a highly ordered average structure, it tends to be subject to the influence of local randomness. We performed local structure analysis by using atomic pair-distribution function (PDF). The Nb-O bond clearly appeared in the observed distribution for NaNbO, but degraded in that for AgNbO. The difference of local structures causes different successive phase transitions for the Nb-related perovskite materials.
and KNbO solid solutionYoneda, Yasuhiro; Kohara, Shinji*; Kumada, Nobuhiro*; Wada, Satoshi*
Japanese Journal of Applied Physics, 53(9S), p.09PD01_1 - 09PD01_5, 2014/09
Times Cited Count：3 Percentile：13.34(Physics, Applied)The atomic-scale structure of solid solution of BaTiO (BT) and KNbO (KN) has been studied using high-energy X-ray diffraction, X-ray absorption fine structure, and atomic pair-distribution function analysis techniques. We prepared BT-KN solid solution through KNbTiO
, in which Ti and Nb atoms are arranged randomly. The average structure of BT-KN solid solution was cubic structure and the local strcuture is also reproduced by the cubic structure. It is rare that a solid solution synthesized from ferroelectric materials has a local strcuture of a paraelectric material. Since the original correlation of BT or KN was lost, ferroelectricity disappeared in the BT-KN solid solution.
Yoneda, Yasuhiro; Fu, D.*; Kohara, Shinji*
Journal of Physics; Conference Series, 502(1), p.012022_1 - 012022_4, 2014/04
Times Cited Count：14 Percentile：97.93(Materials Science, Multidisciplinary)NaNbO has an antiferroelectric structure at room temperature and finds important technological applications. It exhibits an unusual complex sequence of temperature- and pressure-driven structural phase transitions. NaNbO shows unambiguous evidence for the presence of the ferroelectric 
phase coexisting with an antiferroelectric phase (
) over a wide range of temperatures. We have carried out atomic pair-distribution function (PDF) analysis on NaNbO to understand the phase transitions. High-energy X-ray PDF using powder samples were carried out at the SPring-8, which is provided to become rhombohedral structure if -site atoms did order and to become antiferroelectric phase if -site atoms did disorder.
nanoparticlesYoneda, Yasuhiro; Kohara, Shinji*; Kato, Kazumi*
Japanese Journal of Applied Physics, 52(9), p.09KF01_1 - 09KF01_5, 2013/09
Times Cited Count：8 Percentile：34.42(Physics, Applied)The atomic-scale structure of nanocrystalline BaTiO powders has been studied using high-energy X-ray diffraction, X-ray absorption fine structure, and the atomic pair-distribution function technique. The studies show that the materials are well-ordered at nanometer length distance. The three-dimensional atomic ordering in BaTiO is cubic-like on average, but locally shows slight distortions of a tetragonal-type, similar to that occurring in the coarsegrained bulk crystals. Ferroelectric coherence is facilitated in part by control of particle morphology. The spatial extent of cooperative ferroelectric distortions is found to be degraded in nanometer-sized building blocks.
and TbFeYoneda, Yasuhiro; Kohara, Shinji*; Ito, Masayoshi*; Abe, Hiroshi; Takeuchi, Mitsuaki*; Uchida, Hirohisa*; Matsumura, Yoshihito*
Transactions of the Materials Research Society of Japan, 38(1), p.109 - 112, 2013/03
We performed local structure analysis of SmFe and TbFe in the crystallization process from amorphous by using synchrotron X-ray pair-distribution function (PDF) method. The giant mangetostrictive materials of these compounds can be controlled its property by ion irradiation. In amorphous TbFe and SmFe, the mosaic block size was small and the short-range order structure owing to Fe-Fe network maintained. In crystalline SmFe, a rigid long-range order structure of Fe-Fe and Sm-Sm network coexisted and it had a large mosaic block size. On the other hand, in crystalline TbFe, Fe-Fe network degraded by Tb-Tb network owing to its lattice tolerance.
WOYoneda, Yasuhiro; Kohara, Shinji*; Takeda, Hiroaki*; Tsurumi, Takaaki*
Japanese Journal of Applied Physics, 51(9), p.09LE06_1 - 09LE06_6, 2012/09
Times Cited Count：15 Percentile：51.2(Physics, Applied)Local structure analysis of BiWO was performed by high-energy X-ray atomic pair-distribution function (PDF) analysis. We found a deviation between local and average structures owing to the different coherence length between BiO and WO layers. Bi atoms were displaced toward the 
-axis of the orthorhombic 
structure. The local off-center shift of Bi atoms coupled with thermal factor and negrected in the average structure. The coherence length of BiO layer increased with increasing temperature and splead in the whole crystal when the average structure changed from to 
structure.
phases using high-energy X-ray diffractionYoneda, Yasuhiro; Yoshii, Kenji; Kohara, Shinji*
Transactions of the Materials Research Society of Japan, 37(1), p.73 - 76, 2012/03
The structures and phase transitions of AgNbO were investigated using high-energy X-ray powder diffraction. Bragg reflections have revealed the high temperature M-O, O-T, and T-C phase transitions but have not given any significant evidence of low temperature M
-M and M-M ones. The existence of structural disorder in the T and O phases was indicated by diffuse scattering. Here we again confirm the average structure of AgNbO. The refined structure was essentially the same as previous reports. With isotropic thermal parameters, refinements of the structures at most temperatures resulted in larger Ag thermal parameters. Disorder feature of Ag coupled with the thermal parameters and exhibit as diffuse scattering in T and O phases.
Obara, Satoshi; Wakai, Takashi; Asayama, Tai; Yamada, Yoshiyuki*; Nakazawa, Takanori*; Yamazaki, Masayoshi*; Hongo, Hiromichi*
Tetsu To Hagane, 96(4), p.172 - 181, 2010/04
This paper describes the effect of heat treatment on mechanical properties of 9Cr-W-Mo-V-Nb steel as a part of development of high Cr steel for fast breeder reactor (FBR). The effects of normalizing temperature and tempering temperature and time on creep properties were investigated from the viewpoint of microstructures. Creep strength increased with increase in normalizing temperature from 950
C to 1200C. The microstructural factors that improve creep strength are increased amount of MX which precipitated during tempering process and increased dislocation density. In addition, coarsening of prior austenite grain size also contribute to increasing creep strength. Although creep rupture time of 780C-1h tempering specimen was greater than that of 700C-1h and 750C-1h tempering specimen in a long-term region exceeding 20000h at 650C, creep ductility and reduction of area of the former remarkably degraded compared to those of the latter.
O
Hayakawa, Hironori*; Morimoto, Masanori*; Ikeda, Naoshi*; Yoneda, Yasuhiro; Kohara, Shinji*; Yoshii, Kenji; Matsuo, Yoji*; Michiuchi, Takamasa*; Mori, Shigeo*
Transactions of the Materials Research Society of Japan, 34(1), p.51 - 54, 2009/05
We have recently reported that LuFeO becomes ferroelectric below 330 K, owing to a charge-ordering transition of Fe ions. As details of the properties of this material have not been reported so far, we have investigated its local structure in the ferromagnetic phase by means of synchrotron X-ray diffraction. The analysis of pair-distribution function showed the existence of displacement of Lu atoms; this structure is different from the average structure of this materials known thus far. This result encourages a detailed reinvestigation of crystal structure of LuFeO. We also show the results obtained from some other experimental methods, such as dielectric measurement and electron diffraction.
-BaTiO mixtureYoneda, Yasuhiro; Yoshii, Kenji; Kohara, Shinji*; Kitagawa, Shuji*; Mori, Shigeo*
Japanese Journal of Applied Physics, 47(9), p.7590 - 7594, 2008/09
Times Cited Count：24 Percentile：65.66(Physics, Applied)Local structure analysis of (1-
)BiFeO-BaTiO mixture was carried out by synchrotron radiation X-ray pair-distribution function (PDF) method. The PDF peak is resolved as a doublet due to the presence of two distinct bond length, Bi-O and Ba-O. Cubic perovskite lattice of (1-)BiFeO-BaTiO solid solution distorts locally to accomodate the distinct Bi-O and Ba-O bond lengths.
Yamaguchi, Akira*; Takata, Takashi*; Ohshima, Hiroyuki; Kohara, Yoshitake*
Proceedings of 16th International Conference on Nuclear Engineering (ICONE-16) (CD-ROM), 8 Pages, 2008/05
Sodium-water reaction (SWR) is a design basis accident of a Sodium Fast Reactor (SFR). A breach of the heat transfer tube in a steam generator (SG) results in contact of liquid sodium with water. In this paper, a new computer program has been developed and the SWR in a counter-flow diffusion flame is studied by a numerical simulations and an experiment. The experiment is designed with the numerical simulation so that the stable reaction flame is maintained for long time and physical and chemical quantities are measured. From the comparison of analysis and experiment, there exist discrepancies that may be caused by the assumptions of chemical reaction. Hence, a new experiment is proposed to enhance the measurement accuracy and to investigate the reason of the disagreement. The authors propose a depressurized experiment. With the depressurization, it is expected the flame location can be controlled and the reaction region becomes thicker because of decrease in reactant gas density.
Yamasaki, Chisato*; Murakami, Katsuhiko*; Fujii, Yasuyuki*; Sato, Yoshiharu*; Harada, Erimi*; Takeda, Junichi*; Taniya, Takayuki*; Sakate, Ryuichi*; Kikugawa, Shingo*; Shimada, Makoto*; et al.
Nucleic Acids Research, 36(Database), p.D793 - D799, 2008/01
Times Cited Count：52 Percentile：71.15(Biochemistry & Molecular Biology)Here we report the new features and improvements in our latest release of the H-Invitational Database, a comprehensive annotation resource for human genes and transcripts. H-InvDB, originally developed as an integrated database of the human transcriptome based on extensive annotation of large sets of fulllength cDNA (FLcDNA) clones, now provides annotation for 120 558 human mRNAs extracted from the International Nucleotide Sequence Databases (INSD), in addition to 54 978 human FLcDNAs, in the latest release H-InvDB. We mapped those human transcripts onto the human genome sequences (NCBI build 36.1) and determined 34 699 human gene clusters, which could define 34 057 protein-coding and 642 non-protein-coding loci; 858 transcribed loci overlapped with predicted pseudogenes.
-ray study of the neutron-rich nuclei of 
U, 
Pu, and 
Cm produced by the (
O, 
O) reactionIshii, Tetsuro; Shigematsu, Soichiro*; Makii, Hiroyuki; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Matsuda, Makoto; Makishima, Akiyasu*; Shizuma, Toshiyuki; Kaneko, Junichi*; et al.
Physics of Atomic Nuclei, 70(8), p.1457 - 1461, 2007/08
Times Cited Count：9 Percentile：56.35(Physics, Nuclear)We have measured deexcitation rays in the neutron-rich nuclei of U, Pu and Cm. These nuclei were produced by the (O, O) two-neutron transfer reactions with a 200, 162 and 162 MeV O beams and a 
U, 
Pu and 
Cm targets, respectively, using the tandem accelerator at Tokai, Japan. The rays in residual nuclei were measured by taking coincidence with scattering particles using Si 
-
detectors. We have identified rays in U, Pu and Cm by selecting the kinetic energies of O particles which correspond to the excitation energies in these nuclei below their neutron separation energies. The ground-state bands of U, Pu and Cm were established up to 12
states and the 
octupole band of U was established up to 9
state. Because the deformations of these nuclei are well developed, the moments of inertia reflect the pairing gap, which is expected to be smaller, resulting in a larger moment of inertia, at the deformed shell closure. We have found that the moment of inertia of the ground-state band of Cm
is considerably larger than that of Cm
. This fact supports the existence of the deformed subshell closure at 
in Cm isotopes. On the other hand, the moment of inertia of Pu was found to be smaller than that of Pu
, which suggests that the deformed subshell closure at weakens or disappears in Pu isotopes. These results are consistent with the prediction by a cranking model calculation.
SbTe
; Ring statistics analogy between the crystal and amorphous statesKohara, Shinji*; Kato, Kenichi*; Kimura, Shigeru*; Tanaka, Hitoshi*; Usuki, Takeshi*; Suzuya, Kentaro; Tanaka, Hiroshi*; Moritomo, Yutaka*; Matsunaga, Toshiyuki*; Yamada, Noboru*; et al.
Applied Physics Letters, 89(20), p.201910_1 - 201910_3, 2006/11
Times Cited Count：204 Percentile：97.88(Physics, Applied)The three-dimensional atomic configuration of amorphous GeSbTe were derived by reverse Monte Carlo simulation with synchrotron-radiation X-ray diffraction data. The authors found that amorphous GeSbTe can be regarded as "even-numbered ring structure", because the ring statistics is dominated by four- and six-fold rings analogous to the crystal phase. On the other hand, the formation of Ge-Ge homopolar bonds in amorphous GeTe constructs both odd- and even-numbered rings. They believe that the unusual ring statistics of amorphous GeSbTe is the key for the fast crystallization speed of the material.
Nb)O ferroelectricsYoneda, Yasuhiro; Suzuya, Kentaro; Mizuki, Junichiro; Kohara, Shinji*
Journal of Applied Physics, 100(9), p.093521_1 - 093521_4, 2006/11
Times Cited Count：12 Percentile：42.51(Physics, Applied)no abstracts in English
