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Journal Articles

Anomalous vortex dynamics in the spin-triplet superconductor UTe$$_2$$

Tokiwa, Yoshifumi; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Yanase, Yoichi*; Haga, Yoshinori; et al.

Physical Review B, 108(14), p.144502_1 - 144502_5, 2023/10

The vortex dynamics in the spin-triplet superconductor, UTe$$_2$$, are studied by measuring the DC electrical resistivity with currents along the $$a$$-axis under magnetic fields along the $$b$$-axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.

Journal Articles

Field induced multiple superconducting phases in UTe$$_2$$ along hard magnetic axis

Sakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori

Physical Review Letters, 130(19), p.196002_1 - 196002_6, 2023/05

 Times Cited Count:0 Percentile:90.46(Physics, Multidisciplinary)

The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields ($$H$$) along the hard magnetic $$b$$-axis using a high-quality single crystal with $$T_{rm c}$$ = 2.1 K. Simultaneous electrical resistivity and AC magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the $$H^{ast}$$ of $$sim15$$ T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near $$H^{ast}$$, indicating an intermediate SC phase characterized by small flux pinning forces.

Journal Articles

Numerical experiments on dispersion of radionuclides in the ocean released from the Fukushima Daiichi Nuclear Power Plant

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; In, Teiji*; Ishikawa, Yoichi*; Nakayama, Tomoharu*; Shima, Shigeki*; Awaji, Toshiyuki*

Reports of Research Institute for Applied Mechanics, Kyushu University, (143), p.111 - 117, 2012/09

Because of the Fukushima Dai-ichi Nuclear Power Plant disaster, some radionuclides were released into the ocean from the Fukushima Dai-ichi Nuclear Power Plant. In response to this situation, numerical experiments were carried out at Japan Atomic Energy Agency using an oceanic dispersion model and an ocean general circulation model to estimate an effect of the radionuclides on marine environment. It was suggested that the radionuclides deposited from the atmosphere mainly in the middle of March after the disaster spread over a comparatively wide area of the Pacific Ocean east of Japan. On the other hand the radionuclides directly released into the ocean from the Fukushima Dai-ichi Nuclear Power Plant were carried along the coast and then spread along the Kuroshio extension.

Journal Articles

Flux pinning properties of correlated pinning at low temperatures in ErBCO films with inclined columnar defects

Awaji, Satoshi*; Namba, Masashi*; Watanabe, Kazuo*; Kai, Hideki*; Mukaida, Masashi*; Okayasu, Satoru

Journal of Applied Physics, 111(1), p.013914_1 - 013914_4, 2012/01

 Times Cited Count:24 Percentile:69.68(Physics, Applied)

The effect of $$c$$-axis correlated pinning on the critical current density $$J$$$$_{c}$$ at low temperatures under high magnetic fields was investigated on the basis of the transport measurements of $$J$$$$_{c}$$ and irreversibility field B$$_{irr}$$ properties of an ErBa$$_{2}$$Cu$$_{3}$$O$$_{y}$$ film with inclined columnar defects. The contribution of correlated pinning on $$J$$$$_{c}$$ decreased drastically with decreasing temperature under high magnetic fields above the matching field. At low temperatures, the presence of a matching field limited the pinning force for correlated pinning, while the ratio of the maximum pinning force of the correlated pinning to the random one was proportional to the inverse of B$$_{irr}$$. In order to improve the critical current properties at low temperatures under high magnetic fields, an increase in the matching field and/or the introduction of strong random pinning are effective.

Journal Articles

Preliminary numerical experiments on Oceanic dispersion of $$^{131}$$I and $$^{137}$$Cs discharged into the ocean because of the Fukushima Daiichi Nuclear Power Plant disaster

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; In, Teiji*; Ishikawa, Yoichi*; Nakayama, Tomoharu*; Shima, Shigeki*; Awaji, Toshiyuki*

Journal of Nuclear Science and Technology, 48(11), p.1349 - 1356, 2011/11

AA2011-0314.pdf:0.68MB

 Times Cited Count:173 Percentile:99.79(Nuclear Science & Technology)

Numerical experiments were carried out to predict the spreading of $$^{131}$$I and $$^{137}$$Cs released into the ocean due to the Fukushima Daiichi Nuclear Power Plant incident. Results in the numerical experiments were in good agreement with the concentrations of $$^{131}$$I and $$^{137}$$Cs in the monitoring data. It was suggested that the high $$^{131}$$I concentration detected in the young lancefish caught off Kitaibaraki city was due to the deposition from the atmosphere. The numerical experiments suggest that the deposition of radionuclides released into the atmosphere in the middle March largely effected the concentrations of radionuclides east of Japan in the Pacific Ocean.

Journal Articles

A Study of released radionuclide in the coastal area from a discharge pipe of nuclear fuel reprocessing plant in Rokkasho, Aomori, Japan

Kobayashi, Takuya; In, Teiji*; Ishikawa, Yoichi*; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Awaji, Toshiyuki*; Togawa, Orihiko

Progress in Nuclear Science and Technology (Internet), 2, p.682 - 687, 2011/10

When the reprocessing plant is in routine operation, radionuclides are released to the coastal ocean as scheduled. Released radionuclides migrate in the ocean by physical, chemical and biological processes. Thus, for environmental safety, it is important to understand the migration behavior due to routine releases of radionuclides to the coastal ocean from the reprocessing plant. A numerical simulation model system that consists of an ocean general circulation model and a particle random-walk model to describe the radionuclide migration behavior in Rokkasho coastal region has been developed. The particle random-walk model, SEA-GEARN, calculates the radionuclides migration in the ocean. The system has been applied to simulate the nowcast of Rokkasho coastal region in 2007 and hypothetical radionuclide release has been carried out.

Journal Articles

Cooperative behavior of the random and correlated pinning in Er123 films with columnar defects

Awaji, Satoshi*; Namba, Masashi*; Watanabe, Kazuo*; Ito, Shun*; Aoyagi, Eiji*; Kai, Hideki*; Mukaida, Masashi*; Okayasu, Satoru

IEEE Transactions on Applied Superconductivity, 21(3), p.3192 - 3195, 2011/06

 Times Cited Count:5 Percentile:33.82(Engineering, Electrical & Electronic)

The flux pinning behaviors for the heavy ion irradiated Er123 films are investigated based on the detailed $$J$$$$_{rm c}$$ ($$B$$, $$T$$, $$theta$$) properties. The double peaks of $$F$$$$_{rm p}$$ curves for $$B$$//c appear in case of the matching field of 0.3 T along $$c$$-axis and 1.7 T tilted from $$c$$-axis. In addition, the peaks on $$J$$$$_{rm c}$$ ($$theta$$) at $$theta$$ = 0$$^{circ}$$ (B//c), which originate from the columnar defects, decrease with increasing magnetic field but increase again near the irreversibility field. We found that the cooperation model of the $$c$$-axis correlated and random pinning centers can describe the observed double peak behavior of $$F$$$$_{rm p}$$(B) and the angular dependence of $$J$$$$_{rm c}$$ related to the correlated pinning.

Journal Articles

Stress/strain effects on industrial superconducting composites

Ito, Takayoshi; Harjo, S.; Osamura, Kozo*; Hemmi, Tsutomu; Awaji, Satoshi*; Machiya, Shutaro*; Oguro, Hidetoshi*; Nishijima, Gen*; Takahashi, Koki*; Matsui, Kunihiro; et al.

Materials Science Forum, 681, p.209 - 214, 2011/05

 Times Cited Count:1 Percentile:52.96

Journal Articles

Development of a system for the prediction of radionuclide migration in the off Shimokita region and its case study

Kobayashi, Takuya; In, Teiji*; Ishikawa, Yoichi*; Matsuura, Yasutaka*; Shima, Shigeki*; Nakayama, Tomoharu*; Awaji, Toshiyuki*; Kawamura, Hideyuki; Togawa, Orihiko

Nihon Genshiryoku Gakkai Wabun Rombunshi, 7(2), p.112 - 126, 2008/06

The radionuclides migration forecasting system in the off Shimokita region has been developed to predict the routine and accidental releases of liquid radioactive wastes during the operations of a spent nuclear fuel reprocessing plant in Aomori prefecture, Japan. The results obtained from the case studies are as follows; (1) The ocean general circulation model by using the techniques of data assimilation and nesting reproduced well the flow pattern of a coastal area. (2) The estimated internal dose due to ingestion of marine products from hypothetical release of $$^{3}$$H was 0.45 $$mu$$Sv/y. (3) The results of hypothetical release of $$^{137}$$Cs showed that about four percent of the whole deposited on the seabed after a 60-day calculation. The concentration of $$^{137}$$Cs of hypothetical release from the off Shimokita region is the same or less than that of global fallout measured at the same area.

Journal Articles

The Oceanic forecasting system near the Shimokita Peninsula, Japan

In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko; Toyoda, Takahiro*

Proceedings of International Symposium on Environmental Modeling and Radioecology, p.58 - 64, 2007/03

The northwestern part of the Pacific Ocean off the Shimokita Peninsula assumes a complex water mass structure. It is necessary to accurately reproduce the striking circulation patterns and the complicated water mass structures in this area with an ocean general circulation model. We have planned to make use of a one-way nesting method. To initialize the forecast system, we use a 4-dimensional variational method of data assimilation. The assimilated data consist of hydrographic observations collected through the Global Temperature-Salinity Profile Program, sea surface temperature and sea surface height data observed by satellites. A forecast experiment on the basis of oceanographic observations made in 2003 illustrates the good performance of our system. We shall focus, in particular, on the shift from the coastal mode to the gyre mode and vice versa.

Journal Articles

Anisotropy of the second peak in magnetization curves of YBa$$_{2}$$Cu$$_{3}$$O$$_{y}$$ single crystals

*; *; *; *; *; *; Asaoka, Hidehito; *

Critical State in Superconductors,Proc. of 1994 Topical Int. Cryogenic Materials Conf., 0, p.179 - 182, 1995/00

no abstracts in English

Journal Articles

Anisotropic properties of the anomalous second peak in the magnetization curves and the irreversibility field of YBa$$_{2}$$Cu$$_{3}$$Oy(6.6≦y≦6.9) single crystals

*; *; *; *; *; *; *; Asaoka, Hidehito; *

Physica C, 251, p.255 - 262, 1995/00

 Times Cited Count:31 Percentile:82.91(Physics, Applied)

no abstracts in English

Journal Articles

Influence of the flux creep on the irreversibility line of YBa$$_{2}$$Cu$$_{3}$$O$$_{y}$$ (6.6$$leq$$y$$leq$$6.9) single crystals

*; *; *; *; *; *; Asaoka, Hidehito; *

Physica C, 235-240, p.2785 - 2786, 1994/00

 Times Cited Count:4 Percentile:34.37(Physics, Applied)

no abstracts in English

Oral presentation

Preliminary calculation of influences on the North Pacific by the nuclear testing around the Bikini Atoll using SEA-GEARN

Matsuura, Yasutaka*; Nakayama, Tomoharu*; In, Teiji*; Gasa, Shinichi*; Shima, Shigeki*; Kobayashi, Takuya; Togawa, Orihiko; Ishikawa, Yoichi*; Awaji, Toshiyuki*

no journal, , 

no abstracts in English

Oral presentation

Development of hindcast and forecast ocean system off Rokkasho, 3; Data assimilation system in northwestern Pacific ocean

Ishikawa, Yoichi*; Awaji, Toshiyuki*; In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Toyoda, Takahiro*; Kobayashi, Takuya; Togawa, Orihiko; Kawamura, Hideyuki

no journal, , 

no abstracts in English

Oral presentation

Development of hindcast and forecast ocean system off Rokkasho, 4; Hindcast experiment on 2003

In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko; Toyoda, Takahiro*

no journal, , 

no abstracts in English

Oral presentation

The Oceanic forecasting system near the Shimokita Peninsula, Japan

In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko; Toyoda, Takahiro*

no journal, , 

The Shimokita Peninsula (hereafter SP)is located at the northeast tip of Honshu (the main island of Japan) and borders on the northwestern part of the North Pacific Ocean (hereafter NWNP) in the east and the Tsugaru Strait (hereafter TS) in the north. It is known that the NWNP off the SP assumes a complex water mass structure. Seawater of Japan Sea origin, called the Tsugaru Warm Water (TWW) component, takes on a characteristic seasonal variation. Conlon (1982) pointed out that during winter and spring, the TWW in the NWNP propagates southward along the coast of the peninsula (the coastal mode), and swirls off the peninsula from summer to autumn (the gyre mode). It is necessary to accurately reproduce the striking circulation patterns and the complicated water mass structures in this area with an ocean general circulation model (OGCM). We need to use a fine-scale grid, probably such as 1-2 km in size to reproduce the water mass structure around the TS and the off the SP in detail. To initialize the forecast system, we use a 4-dimensional variational method of data assimilation. A forecast experiment on the basis of oceanographic observations made in 2003 (a hindcast experiment) illustrates the good performance of our system. We shall focus, in particular, on the shift from the coastal mode to the gyre mode and vice versa.

Oral presentation

Nowcasting/forecasting system of the ocean circulation off Rokkasho village

In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko

no journal, , 

We have been developing an oceanic forecasting/nowcasting system for the coastal area near Rokkasho village, which locates in the northern part of Honshu Island of Japan. Associated with the geographic features, the oceanographic condition in this area is very complicated. Previous observations show that the seasonal variation in this region is characterized by the two different modes: the coastal mode in a cold season in which flow takes a straight path along the Japan coast, and the gyre mode in a warm season in which swirl-like circulation appears. When attempting the accurate nowcast/forecast of this complicated regional circulation, a downscaling method is an effective approach since it enables us to use such a high resolution 4-dimensional variational data assimilation system. In fact, our forecast result using the high resolution data assimilation system demonstrates the good performance of reproducing both modes in a hindcast sense.

Oral presentation

The Simulation on seasonal variation of the Tsugaru Warm Current by the ocean forecasting system off Rokkasho village

In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko

no journal, , 

An oceanic forecasting system for coastal area near Rokkasho village has been developed. A circulation in this area is primarily controlled by the seasonally-varying Tsugaru Warm Current and the Oyashio. Previous observations suggest that seasonal variation in this region is characterized by two different modes: the coastal mode in cold seasons and the gyre mode in warm seasons. To attempt the accurate forecast, a downscaling method is an effective approach because it enables us to use a high resolution 4-dimensional variational data assimilation system. Model results realistically reproduced the seasonal variation of the Tsugaru Warm Current and the Oyashio from May in 2003 to January in 2004.

Oral presentation

Nowcasting/forecasting system of the ocean circulation off Rokkasho Village

In, Teiji*; Ishikawa, Yoichi*; Shima, Shigeki*; Nakayama, Tomoharu*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko

no journal, , 

We have been developing an oceanic nowcasting/forecasting system for the coastal area near Rokkasho village. The seasonal variation in this region is characterized by the coastal mode in a cold season and the gyre mode in a warm season. A downscaling method is an effective approach for the accurate nowcast/forecast, since it enables us to use a high resolution 4-dimensional variational data assimilation. Our results demonstrate the good performance of reproducing both modes.

37 (Records 1-20 displayed on this page)