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Ueno, Yasuhiro*; Aoki, Masaharu*; Fukao, Yoshinori*; Higashi, Yoshitaka*; Higuchi, Takashi*; Iinuma, Hiromi*; Ikedo, Yutaka*; Ishida, Katsuhiko*; Ito, Takashi; Iwasaki, Masahiko*; et al.
Hyperfine Interactions, 238(1), p.14_1 - 14_6, 2017/11
Times Cited Count：3 Percentile：86.59(Physics, Atomic, Molecular & Chemical)Strasser, P.*; Aoki, Masaharu*; Fukao, Yoshinori*; Higashi, Yoshitaka*; Higuchi, Takashi*; Iinuma, Hiromi*; Ikedo, Yutaka*; Ishida, Katsuhiko*; Ito, Takashi; Iwasaki, Masahiko*; et al.
Hyperfine Interactions, 237(1), p.124_1 - 124_9, 2016/12
Times Cited Count：7 Percentile：90.97(Physics, Atomic, Molecular & Chemical)Oshima, Takeshi; Yokoseki, Takashi; Murata, Koichi; Matsuda, Takuma; Mitomo, Satoshi; Abe, Hiroshi; Makino, Takahiro; Onoda, Shinobu; Hijikata, Yasuto*; Tanaka, Yuki*; et al.
Japanese Journal of Applied Physics, 55(1S), p.01AD01_1 - 01AD01_4, 2016/01
Times Cited Count：14 Percentile：54.92(Physics, Applied)Hijikata, Yasuto*; Mitomo, Satoshi*; Matsuda, Takuma*; Murata, Koichi*; Yokoseki, Takashi*; Makino, Takahiro; Takeyama, Akinori; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; et al.
Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.130 - 133, 2015/11
Sakai, Toru; Hijii, Keigo*; Okubo, Susumu*; Ota, Hitoshi*; Nakano, Hiroki*; Miyashita, Seiji*
Applied Magnetic Resonance, 46(9), p.997 - 1002, 2015/09
Times Cited Count：1 Percentile：6.49(Physics, Atomic, Molecular & Chemical)The S=1/2 kagome-lattice antiferromagnet is investigated by the numerical diagonalization of 18-spin finite-size cluster. The matrix elements proportional to the intensity of the singlet-triplet ESR transition are calculated in the presence of the Dzyaloshinsky-Moriya interaction. Some angle-dependent selection rules is also proposed.
Saito, Toru; Okubo, Toshikazu*; Izumi, Keisuke*; Okawa, Yoshinao*; Kobayashi, Norihiro*; Yamazaki, Toru; Kawano, Katsumi; Isono, Takaaki
Teion Kogaku, 50(8), p.400 - 408, 2015/08
Aramid fiber-reinforced plastic (AFRP) has been developed as a structural material that has the advantages of light weight and high strength. In this study, tensile tests were carried out to measure the tensile properties of AFRP rod on the market for reinforcement of concrete at room temperature, 77 K and 4.2 K. Especially at cryogenic temperatures, it is difficult to perform a tensile test of the bar because the specimen slips through the jig grip. To prevent the rod from slipping, tensile tests were carried out with some filling conditions. The applicable and appropriate tensile test conditions were established by modifying the jig grip, treating the surface of the rod and using cryogenic epoxy infill to grip the rod. They were more than 1100 MPa. Additionally, the AFRP rod included a temperature dependence in which the Young's modulus increased as the test temperature decreased. It was confirmed that the Young's modulus increased because aramid fiber was more dominant than epoxy.
Kokubo, Nobuhito*; Miyahara, Hajime*; Okayasu, Satoru; Nojima, Tsutomu*
Journal of the Physical Society of Japan, 84(4), p.043704_1 - 043704_4, 2015/04
Times Cited Count：4 Percentile：34.89(Physics, Multidisciplinary)We report on the direct observation of vortex states confined in equilateral and isosceles triangular dots of weak pinning amorphous superconducting thin films with a scanning superconducting quantum interference device microscope. The observed images illustrate not only pieces of a triangular vortex lattice as commensurate vortex states, but also incommensurate vortex states including metastable ones. We comparatively analyze vortex configurations found in different sample geometries and discuss the symmetry and stability of commensurate and incommensurate vortex configurations against deformations of the sample shape.
Kokubo, Nobuhito*; Okayasu, Satoru; Nojima, Tsutomu*; Tamochi, Hirotaka*; Shinozaki, Bunju*
Journal of the Physical Society of Japan, 83(8), p.083704_1 - 083704_5, 2014/08
Times Cited Count：15 Percentile：67.23(Physics, Multidisciplinary)Okubo, Seisuke*; Hikima, Ryoichi; Hirano, Toru*; Matsui, Hiroya
JAEA-Research 2010-031, 45 Pages, 2010/10
JAEA-Research-2010-031.pdf:1.22MB
Rock shows time-dependent behavior such as creep/relaxation. With respect to high-level radioactive waste disposal, knowledge of the long-term mechanical stability of shafts and galleries excavated in rock are required, not only during construction and operation but also over a period of thousands of years after closure. Therefore, it is very important to understand the time-dependent behavior of rock for evaluating long-term mechanical stability. The purpose of this study is determining the mechanisms of time-dependent behavior of rock by the precise test, observation and measurement, to develop methods for evaluating long-term mechanical stability. In previous work, testing techniques have been established and basic evaluation methods were developed. Recently, some parameters needed for simulation of time-dependent behavior were determined at the Mizunami underground research facilities. However, we did not have enough data to check on the reliability of the evaluation method for these parameters. This report describes the results of the activities in fiscal year 2009. In Chapter 1, we provide an overview and the background to this study. In Chapter 2, the results of the long-term creep test on Tage tuff, started in fiscal year, 1997 are described. In Chapter 3, methods for obtaining parameters of the constitutive equation for rock are reviewed and summarized. The time dependent behavior of Toki granite and Inada granite (40-80 
C) are also summarized based on data obtained prior to the previous fiscal year. In Chapter 4, the FEM analysis implemented with a generalized variable-compliance-type constitutive equation carried out to clarify the long-term behavior of Toki granite is described. Finally, based on the numerical analysis, an in situ testing method is proposed.
Kokubo, Nobuhito*; Okayasu, Satoru; Kanda, Akinobu*; Shinozaki, Bunju*
Physical Review B, 82(1), p.014501_1 - 014501_7, 2010/07
Times Cited Count：33 Percentile：76.15(Materials Science, Multidisciplinary)Direct observation of vortices by the scanning SQUID microscopy was made on large mesoscopic disks of an amorphous MoGe thin film. Owing to the weak pinning nature of the amorphous film, vortices are able to form geometry induced (quasi-)symmetric configurations of polygons and concentric shells in the large disks. Systematic measurements made on selected disks allow us to trace not only how the vortex pattern evolves with magnetic field, but also how the vortex polygons change in size and rotate with respect to the disk center. The results are in good agreement with theoretical considerations for mesoscopic disks with sufficiently large diameter. A series of vortex images obtained in a disk with a pinning site reveals a unique line of symmetry in vortex configurations, resulting in modifications of the shell filling rule and the magic number.
Nakatsuka, Toru; Nakano, Yoshihiro; Okubo, Tsutomu
Nihon Genshiryoku Gakkai Wabun Rombunshi, 9(2), p.139 - 149, 2010/06
The viability of fuel assembly designs of Reduced-Moderation Water Reactor (RMWR) with fewer kinds of plutonium enrichment of MOX fuel which may result in high local peaking factor in peripheral rods were assessed in the present report. Critical powers of 217-rod bundles with peripheral peaks for upper and lower MOX regions of double-flat core of the RMWR were calculated by a subchannel analysis code NASCA. Peripheral peaking with the corresponding local peaking factor for the uniform plutonium enrichment design yields almost the same critical power as for the flat power distribution. Reduction in fuel fabrication burden may be possible by decreasing the number of the kind of plutonium fuel enrichment while maintaining the same thermal-hydraulic margin as the fuel assembly design with five enrichment types of MOX fuels.
Okubo, Seisuke*; Hirano, Toru; Matsui, Hiroya
JAEA-Research 2009-020, 36 Pages, 2009/08
JAEA-Research-2009-020.pdf:9.18MB
On the radioactive waste disposal, the long-term mechanical stability of tunnel was required. Therefore, we have been developing the method evaluating the stability. This report describes the works in the FY2008. Chapter 1 is the overview. Chapter 2 is the result of long-term creep test on Tage tuff. The strain was increasing at very low speed and the strain rate was decreasing following elapsed time to the powers of -0.9. This behavior is likely to short-term creep. In Chapter 3, the control program was extended to conduct the generalized relaxation test along any relaxation pattern. Then, that test of Toki granite was carried out successfully. The parameters in the variable-compliance-type constitutive equation for Toki granite were deduced. In Chapter 4, parameter-obtaining methods for the constitutive equation were reviewed and criticized. In the final part, an idea of new rock characterization where time-dependent behavior of rock is considered as the important factor was proposed.
Kokubo, Nobuhito*; Okayasu, Satoru; Shinozaki, Bunju*
Physica C, 468(15-20), p.1316 - 1318, 2008/09
Times Cited Count：6 Percentile：30.34(Physics, Applied)We have investigated spatial distributions of vortices induced in small superconducting disks of amorphous MoGe. Scanning SQUID microcopy allows us to observe directly magnetic distributions near the surface of the disks. Results on disks with diameter 0.05 mm demonstrate that quasi-symmetric distributions imposed by the circle geometry appear for vorticity up to 5. Meanwhile, for vorticity more than 6, vortices form an unique shell structure, in which one vortex is located in the center and others form a circle around. The critical vorticity for this structural transition is consistent with results on Nb disks imaged by the magnetic decoration experiments.
Okubo, Seisuke*; Seno, Yasuhiro*; Hirano, Toru; Nakama, Shigeo; Matsui, Hiroya
JAEA-Research 2008-065, 51 Pages, 2008/08
JAEA-Research-2008-065.pdf:2.9MB
This report describes the results of the works in the fiscal year 2007. In Chapter 1, we described the overview and background of this study. In Chapter 2, the result of continuing creep test of Tage tuff which was started from the fiscal year 1997 was described. Although there was some annual variability, the precious data were obtained. In Chapter 3, the control program for the generalized relaxation test was developed. The generalized relaxation test of Toki granite was conducted in order to get basically data. In Chapter 4, the extended constitutive equation of variable compliance was analytically discussed. Using the data obtained in Chapter 3, the parameters of Toki granite of the constitutive equation were obtained and numerical simulation was conducted.
Okubo, Seisuke*; Seno, Yasuhiro; Nakama, Shigeo; Sato, Toshinori*; Hirano, Toru
JAEA-Research 2007-088, 118 Pages, 2008/03
JAEA-Research-2007-088.pdf:27.7MB
This report describes the results of the works in the FY2005 and 2006. In Chapter 2, as the fundamental study on time-dependent behavior, followings were described; (1) The result of continuing creep test of Tage tuff which was started from the FY1997. (2) The results of multi-stage creep test of Inada granite at mid-range temperature. (3) The consideration of the generalized relaxation test. (4) The consideration of new testing method to determine the parameter in the constitutive equation supposed by Okubo. In Chapter 3, followings were described; (1) The results of rock mechanical tests of Toki granite. (2) The results of obtained parameters for the constitutive equation considering time-dependent behavior by mechanical tests and numerical simulations. Furthermore, in this report, following two related studies were attached in appendix; (1) Study on evaluating the effects of scatter in in-situ rock properties. (2) Study on new rock classification method considering long-term behavior of rock mass.
Nishio, Taichiro*; Okayasu, Satoru; Suzuki, Junichi; Kokubo, Nobuhito*; Kadowaki, Kazuo*
Physical Review B, 77(5), p.052503_1 - 052503_4, 2008/02
Times Cited Count：16 Percentile：56.61(Materials Science, Multidisciplinary)We have observed the magnetic field distribution of a vortex generated in amorphous (
)-MoGe thin films with various thicknesses (
) (
, where is the penetration depth) with a scanning SQUID microscope. From analyses of the field distribution as functions of the film thickness and temperature, it is found that an effective in-plane penetration depth (
) extends with descreasing d, in accordance with the Pearl's prediction =2
/. Temperature dependence of is also consistent with the two-fluid model involving the Pearl's prediction.
Hirano, Toru; Seno, Yasuhiro; Nakama, Shigeo; Okubo, Seisuke*
Dai-37-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.397 - 402, 2008/01
Toki granite was tested to obtain parameters for the constitutive equation and numerical simulations were carried out. The testing method was uniaxial compressive loading at the moderate a constant strain rate that is decreased after yielding to obtain the complete stress-strain curve. In addition, two kinds of the strain rate were alternately switched to obtain the parameter 
from one specimen. The represents the strength time-dependence in the constitutive equation. Based on and the complete stress-strain curve, second parameter 
can be calculated by numerical simulations. The accounts for the behavior after yielding. According to the results, Toki granite has =52 and =60. Thus shows relatively low time-dependence.
Okayasu, Satoru; Kokubo, Nobuhito*; Kakeya, Itsuhiro*
Physica C, 463-465, p.294 - 296, 2007/10
Times Cited Count：0 Percentile：0(Physics, Applied)A scanning SQUID microsope is a powerful tool for direct observations of vortices. Magnetic sensitivity is high enough, but spacial resolution is limited by the size of pickup coils. To improve the spacial resolution, a trial usage of microprobe on the pickupcoil was achieved. Preliminary results show the improvement of sensitivity, not spacial resolution.
Chikazawa, Yoshitaka; Okano, Yasushi; Hori, Toru*; Okubo, Yoshiyuki*; Shimakawa, Yoshio*; Tanaka, Toshihiko*
Journal of Nuclear Science and Technology, 43(8), p.829 - 843, 2006/08
Times Cited Count：4 Percentile：30.68(Nuclear Science & Technology)In phase II of the feasibility study of commercialized fast reactor cycle systems, we make a concept of a small sodium cooled reactor for a power source of a city with various requirements, such as, safety and economical competitiveness. Various reactor concepts are surveyed and a tank type reactor whose intermediate heat exchanger and primary main pumps are arranged in series is selected. In this study, a compact long life core and a simple reactor structure designs are pursued. The core type is three regional Zr concentration with one Pu enrichment core, the reactor outlet temperature achieves 550C and the reactor electric output increases from 150MWe to 165MWe. The construction cost is much higher than the economical goal in the case of FOAK. But the construction cost in the case of NOAK is estimated to be 85.6% achieving the economical goal.
Iwamura, Takamichi; Uchikawa, Sadao; Okubo, Tsutomu; Kugo, Teruhiko; Akie, Hiroshi; Nakano, Yoshihiro; Nakatsuka, Toru
Nuclear Engineering and Design, 236(14-16), p.1599 - 1605, 2006/08
Times Cited Count：20 Percentile：78.83(Nuclear Science & Technology)In order to ensure sustainable energy supply in the future based on the matured Light Water Reactor (LWR) and coming Mixed Oxide (MOX)-LWR technologies, a concept of Innovative Water Reactor for Flexible Fuel Cycle (FLWR) has been investigated in Japan Atomic Energy Research Agency (JAEA). The concept consists of two parts in the chronological sequence. The first part realizes a high conversion type core concept, which is basically intended to keep the smooth technical continuity from current LWR and coming MOX-LWR technologies without significant technical gaps. The second part represents the Reduced-Moderation Water Reactor (RMWR) core concept, which realizes a high conversion ratio over 1.0 being useful for the long-term sustainable energy supply through plutonium multiple recycling based on the well-developed LWR technologies. The key point is that the two core concepts utilize the compatible and the same size fuel assemblies, and hence, the former concept can proceed to the latter in the same reactor system, based flexibly on the future fuel cycle circumstances during the reactor operation period around 60 years. Investigation on the core for both the parts of the FLWR concepts has been performed, including the core conceptual design, the core characteristics under Pu multiple recycling, the thermal hydraulic investigation in the tight-lattice core, and so forth. Up to the present, promising results have been obtained.
