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Journal Articles

Denudation process of crystalline nappes in a continental collision zone constrained by inversion of fission-track data and thermokinematic forward modeling; An Example from Eastern Nepalese Himalaya

Nakajima, Toru; Kawakami, Tetsuo*; Iwano, Hideki*; Danhara, Toru*; Sakai, Harutaka*

Journal of Geophysical Research; Solid Earth, 127(5), p.e2021JB023630_1  - e2021JB023630_33, 2022/05

 Times Cited Count:1 Percentile:80.99(Geochemistry & Geophysics)

The thermochronological methods were applied to the Higher Himalayan Crystalline (HHC) nappe and the underlying Lesser Himalayan sediments (LHS) to elucidate the denudation process of the middle- and upper-crust of eastern Nepal over the geological time scale. The thermochronological inverse analysis was undertaken for new results of fission-track (FT) age and FT length data of zircon and apatite in order to reconstruct the time-temperature (${it t-T}$) paths in the temperature range of 60-350 degree. Eight ${it t-T}$ paths obtained along the across-strike section showed that the cooling process of the HHC nappe was characterized by following three aspects: (1) gradual cooling followed by rapid cooling and subsequent gradual cooling, (2) northward-younging of the timing of the rapid cooling, (3) gradual cooling followed by ca. 2 Myr rapid cooling in the frontmost part of the HHC nappe. The observed FT ages and ${it t-T}$ paths were then compared with those predicted by forward thermokinematic modeling. The results of the thermokinematic modeling for the Flat-Ramp-Flat MHT model, in which the HHC and the underlying LHS are denudated accompanied with the movement of the Main Himalayan Thrust (MHT), well reproduced the observed ${it t-T}$ paths and FT ages in eastern Nepal. This suggests that the observed FT ages and ${it t-T}$ paths reflect a denudation process driven by the movement of the MHT showing the flat-ramp-flat geometry, and that the denudation rate and its spatial distribution have roughly been constant in eastern Nepal since ca. 9 Ma.

Journal Articles

Characteristics of fault fracture zones of the activated Shionohira Fault and the non-activated Kuruma Fault of the 2011 Fukushima-ken Hamadori Earthquake, Northeast Japan

Aoki, Kazuhiro; Tanaka, Yukumo; Yoshida, Takumi; Shimada, Koji; Sakai, Toru*; Kametaka, Masao*; Seshimo, Kazuyoshi

Oyo Chishitsu, 62(2), p.64 - 81, 2021/06

Co-seismic surface ruptures in the Fukushima-ken Hamadori Earthquake of Mw 6.7 on April 11, 2011 exposed approximately 14 km trending NNW-SSE from Nameishi to northwest of Ishizumi Tsunaki of Tabito Town, Iwaki City and were newly named the Shionohira Fault. However, no surface ruptures appeared along an N-S trending active Kuruma fault extending 5 km south of the Shionohira Fault. Because of the proximity and similar strike, two locations in Shionohira Fault and one location in Kuruma fault were selected as the study area for the fault activity evaluation. The present study reports the results of a series of geological and drilling surveys, core observation, XRD, isotope, and fluid inclusion analyses, and water permeability test. The results obtained from the three locations offer a fundamental data base that can be utilized for fault activity evaluation by summarizing the geological, mineralogical, and fluid property characteristics of fault fracture zone.

JAEA Reports

Annual report on the effluent control of low level liquid waste in Nuclear Fuel Cycle Engineering Laboratories FY2018

Nakano, Masanao; Fujii, Tomoko; Nagaoka, Mika; Inoue, Kazumi; Koike, Yuko; Yamada, Ryohei; Yoshii, Hideki*; Otani, Kazunori*; Hiyama, Yoshinori*; Kikuchi, Masaaki*; et al.

JAEA-Review 2019-045, 120 Pages, 2020/03

JAEA-Review-2019-045.pdf:2.54MB

Based on the regulations (the safety regulation of Tokai Reprocessing Plant, the safety regulation of nuclear fuel material usage facilities, the radiation safety rule, the regulation about prevention from radiation hazards due to radioisotopes, which are related with the nuclear regulatory acts, the local agreement concerning with safety and environment conservation around nuclear facilities, the water pollution control law, and by law of Ibaraki Prefecture), the effluent control of liquid waste discharged from the Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency has been performed. This report describes the effluent control results of the liquid waste in the fiscal year 2018. In this period, the concentrations and the quantities of the radioactivity in liquid waste discharged from the reprocessing plant, the plutonium fuel fabrication facilities, and the other nuclear fuel material usage facilities were much lower than the limits authorized by the above regulations.

JAEA Reports

Annual report on the effluent control of low level liquid waste in Nuclear Fuel Cycle Engineering Laboratories FY2017

Nakano, Masanao; Fujita, Hiroki; Mizutani, Tomoko; Nagaoka, Mika; Inoue, Kazumi; Koike, Yuko; Yamada, Ryohei; Yoshii, Hideki*; Hiyama, Yoshinori*; Otani, Kazunori*; et al.

JAEA-Review 2018-028, 120 Pages, 2019/02

JAEA-Review-2018-028.pdf:2.69MB

Based on the regulations (the safety regulation of Tokai Reprocessing Plant, the safety regulation of nuclear fuel material usage facilities, the radiation safety rule, the regulation about prevention from radiation hazards due to radioisotopes, which are related with the nuclear regulatory acts, the local agreement concerning with safety and environment conservation around nuclear facilities, the water pollution control law, and by law of Ibaraki Prefecture), the effluent control of liquid waste discharged from the Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency has been performed. This report describes the effluent control results of the liquid waste in the fiscal year 2017. In this period, the concentrations and the quantities of the radioactivity in liquid waste discharged from the reprocessing plant, the plutonium fuel fabrication facilities, and the other nuclear fuel material usage facilities were much lower than the limits authorized by the above regulations.

JAEA Reports

Annual report on the effluent control of low level liquid waste in Nuclear Fuel Cycle Engineering Laboratories FY2016

Nakano, Masanao; Fujita, Hiroki; Nagaoka, Mika; Inoue, Kazumi; Koike, Yuko; Yoshii, Hideki*; Hiyama, Yoshinori*; Otani, Kazunori*; Kikuchi, Masaaki*; Sakauchi, Nobuyuki*; et al.

JAEA-Review 2017-037, 119 Pages, 2018/03

JAEA-Review-2017-037.pdf:2.58MB

Based on the regulations (the safety regulation of Tokai Reprocessing Plant, the safety regulation of nuclear fuel material usage facilities, the radiation safety rule, the regulation about prevention from radiation hazards due to radioisotopes, which are related with the nuclear regulatory acts, the local agreement concerning with safety and environment conservation around nuclear facilities, the water pollution control law, and bylaw of Ibaraki Prefecture), the effluent control of liquid waste discharged from the Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency has been performed. This report describes the effluent control results of the liquid waste in the fiscal year 2016. In this period, the concentrations and the quantities of the radioactivity in liquid waste discharged from the reprocessing plant, the plutonium fuel fabrication facilities, and the other nuclear fuel material usage facilities were much lower than the limits authorized by the above regulations.

Journal Articles

Study on In-Vessel Retention (IVR) of unprotected accident for fast reactor, 1; Overview of IVR evaluation in Anticipated Transient without Scram (ATWS)

Suzuki, Toru; Sogabe, Joji; Tobita, Yoshiharu; Sakai, Takaaki*; Nakai, Ryodai

Nihon Kikai Gakkai Rombunshu (Internet), 83(848), p.16-00395_1 - 16-00395_9, 2017/04

no abstracts in English

Journal Articles

Study on In-Vessel Retention (IVR) of unprotected accident for fast reactor, 1; Overview of IVR evaluation in Anticipated Transient without Scram (ATWS)

Suzuki, Toru; Sogabe, Joji; Tobita, Yoshiharu; Sakai, Takaaki*; Nakai, Ryodai

Dai-21-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (USB Flash Drive), 4 Pages, 2016/06

Journal Articles

Ground-state phase diagram of an anisotropic S=1/2 ladder with alternating rung interactions

Tonegawa, Takashi*; Okamoto, Kiyomi*; Hikihara, Toshiya*; Sakai, Toru

Journal of Physics; Conference Series, 683(1), p.012039_1 - 012039_7, 2016/02

 Times Cited Count:2 Percentile:73.48

Employing mainly numerical methods, we explore the ground-state phase diagram of an anisotropic S=1/2 ladder, in which leg interactions are uniform and isotropic, while rung interactions are alternating and have a common Ising-type anisotropy. We determine the phase diagrams in some typical cases.

Journal Articles

Effect of monomer-monomer interactions on the phase diagrams of the S=1/2 distorted diamond type quantum spin chain

Okamoto, Kiyomi*; Tonegawa, Takashi*; Sakai, Toru

Journal of Physics; Conference Series, 683(1), p.012038_1 - 012038_6, 2016/02

 Times Cited Count:2 Percentile:73.48

By use of mainly the exact diagonalization and the level spectroscopy method, we investigate the ground-state phase diagrams of the S=1/2 distorted diamond type quantum spin chain with the monomer-monomer interactions and ferromagnetic interactions. The magnetization plateau at 1/3 of the saturation magnetization was revealed to vanish in the region where the ferromagnetic interaction is rather strong.

Journal Articles

Novel quantum phase transition in the frustrated spin nanotube

Sakai, Toru; Nakano, Hiroki*

Physics Procedia, 75, p.369 - 375, 2015/12

 Times Cited Count:1 Percentile:49.16

The S=1/2 three-leg quantum spin tube is investigated using the numerical diagonalization. The study indicated a new quantum phase transition between the 1/3 magnetization plateau phase and the plateauless one, with respect to the spin anisotropy. The phase diagram is also presented.

Journal Articles

Exotic field induced quantum phase transition of the kagome lattice antiferromagnet

Sakai, Toru; Nakano, Hiroki*

Physics Procedia, 75, p.821 - 828, 2015/12

 Times Cited Count:0 Percentile:0.04

The magnetization process of the S=1/2 kagome-lattice antiferromagnet is investigated using the numerical diagonalization up to 42-spin clusters. The critical exponent analysis confirms the unconventional magnetization behavior around the 1/3 magnetization plateau-like anomaly; the field derivative is infinite at the low-field side, while it is zero at the high-field side. We also confirm that a magnetization jump appears at 1/3 of the saturation magnetization in distorted kagome-lattice antiferromagnets.

Journal Articles

Magnetization jump in the magnetization process of the spin-1/2 Heisenberg antiferromagnet on a distorted square-kagome lattice

Nakano, Hiroki*; Hasegawa, Yasumasa*; Sakai, Toru

Journal of the Physical Society of Japan, 84(11), p.114703_1 - 114703_6, 2015/11

 Times Cited Count:26 Percentile:81.54(Physics, Multidisciplinary)

The magnetization process of the spin-1/2 Heisenberg antiferromagnet on the distorted square-kagome lattice is investigated by the large-scale numerical diagonalization method. It is found that a novel magnetization jump appears at 1/3 of the saturation magnetization.

Journal Articles

Evolution of the filamentary 3-Kelvin phase in Pb-Ru-Sr$$_{2}$$RuO$$_{4}$$ Josephson junctions

Kaneyasu, Hirono*; Etter, S. B.*; Sakai, Toru; Sigrist, M.*

Physical Review B, 92(13), p.134515_1 - 134515_5, 2015/10

 Times Cited Count:3 Percentile:16.62(Materials Science, Multidisciplinary)

The evolution of the 3-Kelvin superconductivity phase at the interface between Sr$$_{2}$$RuO$$_{4}$$ and Ru-metal inclusions is discussed for Pb-Ru-Sr$$_{2}$$RuO$$_{4}$$ contacts. Using the Ginzburg-Landau model, the influence of proximity-induced superconductivity in Ru on the topology of the 3-K phase is analysed. Because the s-wave order parameter in Ru favors a 3-K state of trivial topology, the onset temperature of the phase with a nontrivial topology is essentially reduced to the bulk transition temperature.

Journal Articles

Spin nanotubes with the ring exchange interactions

Sakai, Toru; Kasahara, Toshihiro*; Hijii, Keigo*; Ota, Hitoshi*; Nakano, Hiroki*

Synthetic Metals, 208, p.26 - 28, 2015/10

 Times Cited Count:1 Percentile:5.43(Materials Science, Multidisciplinary)

The S=1/2 three-leg spin nanotube with the ring exchange interaction at each plaquette is investigated using the numerical diagonalization of finite-size systems. The previous work suggested that the system without the ring exchange interaction has a spin excitation gap between the singlet ground state and the triplet excitation, because a spontaneous dimerization occurs in the ground state. The present study indicates that as the ring exchange increases, a quantum phase transition occurs at some critical value to another spin gap phase where the pattern of the dimerization is different from the initial one.

Journal Articles

Possible singlet-triplet transition of ESR in the kagome-lattice antiferromagnet

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:7.56(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.

Journal Articles

Perturbation on hyperfine-enhanced $$^{141}$$Pr nuclear spin dynamics associated with antiferroquadrupolar order in PrV$$_2$$Al$$_{20}$$

Ito, Takashi; Higemoto, Wataru; Sakai, Akito*; Nakatsuji, Satoru*; Tsujimoto, Masaki*

Physical Review B, 92(12), p.125151_1 - 125151_5, 2015/09

 Times Cited Count:4 Percentile:16.62(Materials Science, Multidisciplinary)

Journal Articles

Magnetization process of the spin-S kagome-lattice Heisenberg antiferromagnet

Nakano, Hiroki*; Sakai, Toru

Journal of the Physical Society of Japan, 84(6), p.063705_1 - 063705_5, 2015/06

 Times Cited Count:25 Percentile:80.82(Physics, Multidisciplinary)

The magnetization process of the spin-S Heisenberg antiferromagnet on the kagome lattice is studied by the numerical-diagonalization method. Our numerical-diagonalization data for small finite-size clusters with S=1, 3/2, 2 and 5/2 suggest that a magnetization plateau appears at one-third of the height of the saturation in the magnetization process irrespective of S. We discuss the S dependences of the edge fields and the width of the plateau in comparison with recent results by real-space perturbation theory.

Journal Articles

Instability of a ferrimagnetic state of a frustrated $$S$$=1/2 Heisenberg antiferromagnet in two dimensions

Nakano, Hiroki*; Sakai, Toru

Japanese Journal of Applied Physics, 54(3), p.030305_1 - 030305_4, 2015/03

To clarify the instability of the ferrimagnetism which is the fundamental magnetism of ferrite, numerical diagonalization study for the two-dimensional $$S$$=1/2 Heisenberg antiferromagnet with frustration. We find that the ferrimagnetic ground state has the spontaneous magnetization in small frustration.

Journal Articles

Instability of a ferrimagnetic state of a frustrated S=1/2 Heisenberg antiferromagnet in two dimensions

Nakano, Hiroki*; Sakai, Toru

Japanese Journal of Applied Physics, 54(3), p.030305_1 - 030305_4, 2015/03

 Times Cited Count:10 Percentile:45.9(Physics, Applied)

To clarify the instability of the ferrimagnetism which is the fundamental magnetism of ferrite, numerical-diagonalization study is carried out for the two-dimensional S=1/2 Heisenberg antiferromagnet with frustration. We find that the ferrimagnetic ground state has the spontaneous magnetization in small frustration.

Journal Articles

Novel field induced quantum phase transition of the kagome lattice antiferromagnet

Sakai, Toru; Nakano, Hiroki*

Journal of Physics; Conference Series, 568(4), p.042025_1 - 042025_6, 2014/12

 Times Cited Count:0 Percentile:0.05

The kagome-lattice antiferromagnets have attracted a lot of interest in the field of the low-temperature physics. It exhibits some exotic field-induced phenomena, like a magnetization plateau, jump etc. Our previous large-scale yumerical exact diagonalization study on the S=1/2 kagome-lattice antiferromagnet revealed that a novel field-induced phenomenon, "the magnetization ramp", occurs at 1/3 of the saturation magnetization. It is characterized by different critical exponents between the lower-field and higher-field sides of the magnetization curve. In order to clarify unconventional properties around the 1/3 magnetization, we considered some extended lattice models; a distorted kagome lattice and distorted triangular lattice etc. Our numerical exact diagonalization study also indicates that the ground state of the kagome-lattice antiferromagnet is gapless quantum spin liquid.

172 (Records 1-20 displayed on this page)