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Journal Articles

Kondo effect with Wilson fermions

Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suzuki, Kei

Physical Review D, 104(9), p.094515_1 - 094515_11, 2021/11

We investigate the Kondo effect with Wilson fermions. This is based on a mean-field approach for the chiral Gross-Neveu model including four-point interactions between a light Wilson fermion and a heavy fermion. For massless Wilson fermions, we demonstrate the appearance of the Kondo effect. We point out that there is a coexistence phase with both the light-fermion scalar condensate and Kondo condensate, and the critical chemical potentials of the scalar condensate are shifted by the Kondo effect. For negative-mass Wilson fermions, we find that the Kondo effect is favored near the parameter region realizing the Aoki phase. Our findings will be useful for understanding the roles of heavy impurities in Dirac semimetals, topological insulators, and lattice simulations.

Journal Articles

Lattice-fermionic Casimir effect and topological insulators

Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suzuki, Kei

Physical Review Research (Internet), 3(2), p.023201_1 - 023201_23, 2021/06

The Casimir effect arises from the zero-point energy of particles in momentum space deformed by the existence of two parallel plates. For degrees of freedom on the lattice, its energy-momentum dispersion is determined so as to keep a periodicity within the Brillouin zone, so that its Casimir effect is modified. We study the properties of Casimir effect for lattice fermions, such as the naive fermion, Wilson fermion, and overlap fermion based on the M$"o$bius domain-wall fermion formulation, in the $$1+1$$, $$2+1$$, and $$3+1$$ dimensional spacetime with the periodic or antiperiodic boundary condition. An oscillatory behavior of Casimir energy between odd and even lattice size is induced by the contribution of ultraviolet-momentum (doubler) modes, which realizes in the naive fermion, Wilson fermion in a negative mass, and overlap fermions with a large domain-wall height. Our findings can be experimentally observed in condensed matter systems such as topological insulators and also numerically measured in lattice simulations.

Journal Articles

Casimir effect for lattice fermions

Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suzuki, Kei

Physics Letters B, 809, p.135713_1 - 135713_7, 2020/10

 Times Cited Count:2 Percentile:57.67(Astronomy & Astrophysics)

We propose a definition of the Casimir energy for free lattice fermions. From this definition, we study the Casimir effects for the massless or massive naive fermion, Wilson fermion, and (M$"o$bius) domain-wall fermion in 1+1 dimensional spacetime with the spatial periodic or antiperiodic boundary condition. For the naive fermion, we find an oscillatory behavior of the Casimir energy, which is caused by the difference between odd and even lattice sizes. For the Wilson fermion, in the small lattice size of $$N geq 3$$, the Casimir energy agrees very well with that of the continuum theory, which suggests that we can control the discretization artifacts for the Casimir effect measured in lattice simulations. We also investigate the dependence on the parameters tunable in M$"o$bius domain-wall fermions. Our findings will be observed both in condensed matter systems and in lattice simulations with a small size.

Journal Articles

$$D$$ mesons as a probe of Casimir effect for chiral symmetry breaking

Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suenaga, Daiki*; Suzuki, Kei

Physical Review D, 100(3), p.034016_1 - 034016_14, 2019/08

 Times Cited Count:3 Percentile:34.26(Astronomy & Astrophysics)

We propose $$D$$ mesons as probes to investigate finite-volume effects for chiral symmetry breaking at zero and finite temperatures. By using the 2+1-flavor linear sigma model with constituent light quarks, we analyze the Casimir effects for the $$sigma$$ mean fields; the chiral symmetry is rapidly restored by the antiperiodic boundary for light quarks, and the chiral symmetry breaking is catalyzed by the periodic boundary. We also show the phase diagram of the $$sigma$$ mean fields on the volume and temperature plane. For $$D$$ mesons, we employ an effective model based on the chiral-partner structure, in which the volume dependence of $$D$$ mesons is induced by the $$sigma$$ mean fields. We find that $$D_s$$ mesons are less sensitive to finite volume than $$D$$ mesons, which is caused by the insensitivity of $$sigma_s$$ mean fields. An anomalous mass shift of $$D$$ mesons at high temperature with the periodic boundary will be useful in examinations with lattice QCD simulations. The dependence on the number of compactified spatial dimensions is also studied.

Journal Articles

Quantum paramagnet near spin-state transition

Tomiyasu, Keisuke*; Ito, Naoko*; Okazaki, Ryuji*; Takahashi, Yuki*; Onodera, Mitsugi*; Iwasa, Kazuaki*; Nojima, Tsutomu*; Aoyama, Takuya*; Ogushi, Kenya*; Ishikawa, Yoshihisa*; et al.

Advanced Quantum Technologies (Internet), 1(3), p.1800057_1 - 1800057_7, 2018/12

Spin-state transition, also known as spin crossover, plays a key role in diverse systems. In theory, the boundary range between the low- and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that the Sc substitution in LaCoO3 destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co-O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low- and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition.

Journal Articles

Consideration on effective Pu utilization in high conversion type LWR for better transition to FBR cycle

Ishikawa, Nobuyuki; Okubo, Tsutomu

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 4 Pages, 2011/12

It is necessary to consider the transition from LWR to FBR cycle in terms of reactor introduction point of view since the FBR necessitate LWR originated plutonium in its introduction stage. The plutonium necessary for introduction of FBR is supplied from reprocessing of spent fuel of LWR, not only in the form of UOX fuel but also MOX one. In this sense, the MOX spent fuel from LWR plays a role of plutonium supply source for FBR so that it may require effective use of plutonium in LWR in advance for introduction of FBR. The high conversion type LWR (HC-LWR) may be a preferable option for plutonium utilization in LWR especially taking into account the transition to FBR cycle, since it can preserve much amount of plutonium with good isotopic composition for FBR. Considering these points, in this study, the characteristics of HC-LWR are evaluated in terms of effective plutonium utilization for transition to FBR cycle.

JAEA Reports

Research on high conversion type FLWR (HC-FLWR) core

Nakano, Yoshihiro; Fukaya, Yuji; Akie, Hiroshi; Ishikawa, Nobuyuki; Okubo, Tsutomu; Uchikawa, Sadao

JAEA-Research 2009-061, 92 Pages, 2010/03

JAEA-Research-2009-061.pdf:9.5MB

A series of research on a high conversion type innovative water reactor for flexible fuel cycle (FLWR) has been conducted. This FLWR is a boiling water reactor (BWR) with a tight triangular fuel rod lattice and the uranium plutonium mixed oxide (MOX) fuel. FLWR is designed for two types of cores to be developed in succession. The preceding core is a high conversion type FLWR (HC-FLWR) and the other core is Reduced Moderation Water Reactor (RMWR) of which the conversion ratio is more than 1.0. Three design studies and a senario study on HC-FLWR are presented in this report. The first design study is for a representative core. The second one is for a transition core from HC-FLWR to RMWR. In the transition core, both assemblies for HC-FLWR and RMWR exist. The third one is for a core to recycle minor actinides (MAs). Regarding to the scenario study, based on design results of the representative core, effective plutonium utilization in future LWR was considered within general framework.

Journal Articles

Analytical evaluation on dynamical response characteristics of reduced-moderation water reactor with tight-lattice core under natural circulation core cooling

Ishikawa, Nobuyuki; Okubo, Tsutomu

Annals of Nuclear Energy, 36(5), p.650 - 658, 2009/05

 Times Cited Count:7 Percentile:48.67(Nuclear Science & Technology)

The time-domain analyses with TRAC-BF1 code were performed for clarifying the dynamical response characteristics of the reduced-moderation water reactor (RMWR) with tight-lattice core configuration. The response characteristics were evaluated based on the step response basically utilized for dynamical system evaluation. As for the most fundamental dynamical characteristics, the flow response characteristics of single fuel assembly concerning channel flow response characteristics were evaluated. As for a natural circulation flow response, it is clarified that the response is strongly influenced by the effect of two-phase pressure loss on account of high void fraction condition. The reactor power response with reactivity feedback shows quite stable response characteristics on account of the small absolute value of void reactivity feedback coefficient.

Journal Articles

General consideration on effective plutonium utilization in future LWRs

Ishikawa, Nobuyuki; Okubo, Tsutomu

Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9071_1 - 9071_8, 2009/05

In this study, the potential of mixed oxide fueled light water reactors (MOX-LWRs), especially focusing on the high conversion type LWRs (HC-LWRs) such as FLWR are evaluated in terms of both economic aspect and effective use of plutonium. For economics consideration, relative economics positions of MOX-LWRs are clarified comparing the cost of electricity for uranium fueled LWRs (U-LWRs), MOX-LWRs and fast breeder reactors (FBRs) assuming future natural uranium price raise and variation of parameters such as construction cost and capacity factor. Also the economic superiority of MOX utilization against the uranium use is mentioned from the view point of plutonium credit concerning to the front-end fuel cycle cost. In terms of effective use of plutonium, comparative evaluations on plutonium mass balance in the cases of HC-LWR and high moderation type LWRs (HM-LWRs) taking into account plutonium quality (ratio of fissile to total plutonium) constraint in multiple recycling are performed as representative MOX utilization cases. Through this evaluation, the advantageous features of plutonium multiple recycling by HC-LWR are clarified.

Journal Articles

Superconducting MgB$$_2$$ thin film detector for neutrons

Ishida, 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:79.96(Physics, Applied)

The superconducting neutron detector using high-quality $$^{10}$$B-enriched MgB$$_2$$ thin films at higher operating temperatures has been proposed, where a resistance change induced by the nuclear reaction of neutron and $$^{10}$$B in MgB$$_2$$ is used to detect a neutron. Cold neutrons from a nuclear research reactor irradiated the MgB$$_2$$ 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.

Journal Articles

Design and scenario studies on FLWR for effective use of Pu

Iwamura, Takamichi; Ishikawa, Nobuyuki; Okubo, Tsutomu

Proceedings of 4th Asian Specialist Meeting on Future Small-Sized LWR Development, p.11_1 - 11_9, 2007/11

An advanced LWR concept of Innovative Water Reactor for Flexible fuel cycle (FLWR) has been established based on the well-experienced LWR technologies. The feature of this concept is that the high conversion type core (HC-FLWR) with small technical gap from current LWR technologies can be proceed to the breeding type FLWR core, named Reduced-Moderation Water Reactor (RMWR) under the same core configuration and reactor systems. This paper describes the investigations on designs and introduction scenario of FLWR.

JAEA Reports

Report on the 9th Workshop on the Innovative Water Reactor for Flexible Fuel Cycle; March 1, 2006, Koku-kaikan, Minato-ku, Tokyo

Ishikawa, Nobuyuki; Kobayashi, Noboru; Okubo, Tsutomu; Uchikawa, Sadao

JAEA-Review 2006-020, 102 Pages, 2006/07

JAEA-Review-2006-020.pdf:11.72MB

The research on Innovative Water Reactor for Flexible Fuel Cycle (FLWR) has been performed in JAEA for the development of future innovative reactor. The workshop on FLWRs has been held every year since 1998 aiming at information exchange with other organizations such as universities, laboratories, utilities and vendors. The 9th workshop was held on March 1, 2006 with 64 participants. The workshop began with presentation entitled "Activities on Nuclear Science and Engineering Research and Collaboration with Industry in JAEA", followed by presentations entitled "Progress of Research and Development on FLWR" and "On Final Report of Feasibility Study (phase 2) on Commercialized FBR Cycle Systems". Then two lectures followed: "Core and Fuel Design on Super Light Water Reactor" by Tokyo University and "Recent Trends on the Development of Next Generation Nuclear Reactor" by Institute of Applied Energy. This report summarizes the lectures of the workshop.

Journal Articles

Proposal of simplified model of radionuclide release from fuel under severe accident conditions considering pressure effect

Hidaka, Akihide; Kudo, Tamotsu; Ishigami, Tsutomu; Ishikawa, Jun; Fuketa, Toyoshi

Journal of Nuclear Science and Technology, 41(12), p.1192 - 1203, 2004/12

 Times Cited Count:5 Percentile:36.97(Nuclear Science & Technology)

An experimental program VEGA is being performed at JAERI to understand mechanisms of radionuclides release from fuel during severe accidents and to improve source term predictability. The VEGA tests showed that the Cs release rate at 1.0MPa decreased by about 30% compared with that at 0.1MPa. To explain this pressure effect, a numerical release model on 2-stage diffusion that considers the lattice diffusion in grains followed by gaseous diffusion in open pores was newly developed and a simplified model 1/$$sqrt{P}$$ CORSOR-M was derived from the numerical model. The effect of pressure on source term was also estimated for a transient sequence at BWR with JAERI's THALES-2 code in which the simplified model was incorporated. Since the adequacy and applicability of 1/$$sqrt{P}$$ CORSOR-M model were confirmed for the pressures up to 16 MPa through comparison with the VEGA tests and mechanistic models, it is proposed that the model be used for source term analyses.

JAEA Reports

Feasibility Study on Commercialization of Fast Breeder Reactor Cycle Systems Interim Report of Phase II; Technical Study Report for Reactor Plant Systems

Konomura, Mamoru; Ogawa, Takashi; Okano, Yasushi; Yamaguchi, Hiroyuki; Murakami, Tsutomu; Takaki, Naoyuki; Nishiguchi, Youhei; Sugino, Kazuteru; Naganuma, Masayuki; Hishida, Masahiko; et al.

JNC TN9400 2004-035, 2071 Pages, 2004/06

JNC-TN9400-2004-035.pdf:76.42MB

The attractive concepts for Sodium-, lead-bismuth-, helium- and water-cooled FBRs have been created through using typical plant features and employing advanced technologies. Efforts on evaluating technological prospects of feasibility have been paid for these concepts. Also, it was comfirmed if these concepts satisfy design requierments of capability and performance presumed in the feasibilty study on commertialization of Fast Breeder Reactor Systems. As results, it was concluded that the selection of sodium-cooled reactor was most rational for practical use of FBR technologies in 2015.

JAEA Reports

Research and development on reduced-moderation light water reactor with passive safety features (Contract research)

Iwamura, Takamichi; Okubo, Tsutomu; Akie, Hiroshi; Kugo, Teruhiko; Yonomoto, Taisuke; Kureta, Masatoshi; Ishikawa, Nobuyuki; Nagaya, Yasunobu; Araya, Fumimasa; Okajima, Shigeaki; et al.

JAERI-Research 2004-008, 383 Pages, 2004/06

JAERI-Research-2004-008.pdf:21.49MB

The present report contains the achievement of "Research and Development on Reduced-Moderation Light Water Reactor with Passive Safety Features", which was performed by Japan Atomic Energy Research Institute (JAERI), Hitachi Ltd., Japan Atomic Power Company and Tokyo Institute of Technology in FY2000-2002 as the innovative and viable nuclear energy technology (IVNET) development project operated by the Institute of Applied Energy (IAE). In the present project, the reduced-moderation water reactor (RMWR) has been developed to ensure sustainable energy supply and to solve the recent problems of nuclear power and nuclear fuel cycle, such as economical competitiveness, effective use of plutonium and reduction of spent fuel storage. The RMWR can attain the favorable characteristics such as high burnup, long operation cycle, multiple recycling of plutonium (Pu) and effective utilization of uranium resources based on accumulated LWR technologies.

Journal Articles

Excitation and decay of the isovector spin-flip giant monopole resonance via the $$^{208}$$Pb($$^{3}$$He,${it tp}$) reaction at 410 MeV

Zegers, R. G. T.*; Abend, H.*; Akimune, Hidetoshi*; Van den Berg, A. M.*; Fujimura, Hisako*; Fujita, Hirohiko*; Fujita, Yoshitaka*; Fujiwara, Mamoru; Gal$`e$s, S.*; Hara, Keigo*; et al.

Nuclear Physics A, 731, p.121 - 128, 2004/02

 Times Cited Count:11 Percentile:58.28(Physics, Nuclear)

no abstracts in English

Journal Articles

Beam-palarization asymmetries for the $$p$$($$overrightarrow{gamma}$$,$$K$$$$^{+}$$)$$Lambda$$ and $$p$$($$overrightarrow{gamma}$$,$$K$$$$^{+}$$)$$Sigma$$$$^{0}$$ reactions for $$E$$$$_{gamma}$$=1.5-2.4 GeV

Zegers, R. G. T.*; Sumihama, Mizuki*; Ahn, D. S.*; Ahn, J. K.*; Akimune, Hidetoshi*; Asano, Yoshihiro; Chang, W. C.*; Dat$'e$, S.*; Ejiri, Hiroyasu*; Fujimura, Hisako*; et al.

Physical Review Letters, 91(9), p.092001_1 - 092001_4, 2003/08

 Times Cited Count:127 Percentile:95.25(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Evidence for a narrow $$S$$ = +1 Baryon resonance in photoproduction from the neutron

Nakano, Takashi*; Ahn, D. S.*; Ahn, J. K.*; Akimune, Hidetoshi*; Asano, Yoshihiro; Chang, W. C.*; Date, S.*; Ejiri, Hiroyasu*; Fujimura, Hisako*; Fujiwara, Mamoru; et al.

Physical Review Letters, 91(1), p.012002_1 - 012002_4, 2003/07

 Times Cited Count:994 Percentile:99.88(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Excitation and decay of the Isovector giant monopole resonances via the $$^{208}$$Pb($$^{3}$$He,${it tp}$) reaction at 410 MeV

Zegers, R. G. T.; Abend, H.*; Akimune, Hidetoshi*; Van den Berg, A. M.*; Fujimura, Hisako*; Fujita, Hirohiko*; Fujita, Yoshitaka*; Fujiwara, Mamoru; Gal$`e$s, S.*; Hara, Keigo*; et al.

Physical Review Letters, 90(20), p.202501_1 - 202501_4, 2003/05

 Times Cited Count:46 Percentile:85.12(Physics, Multidisciplinary)

no abstracts in English

JAEA Reports

CHF experiments of tight pitch lattice rod bundles under PWR pressure condition for development of reduced moderation water reactor

Araya, Fumimasa; Nakatsuka, Toru; Yoritsune, Tsutomu; Kureta, Masatoshi; Yoshida, Hiroyuki; Ishikawa, Nobuyuki; Sato, Takashi; Watanabe, Hironori; Okubo, Tsutomu; Iwamura, Takamichi; et al.

JAERI-Research 2002-018, 37 Pages, 2002/10

JAERI-Research-2002-018.pdf:2.62MB

no abstracts in English

43 (Records 1-20 displayed on this page)