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Journal Articles

Colossal barocaloric effects in plastic crystals

Li, B.*; Kawakita, Yukinobu; Kawamura, Seiko; Sugahara, Takeshi*; Wang, H.*; Wang, J.*; Chen, Y.*; Kawaguchi, Saori*; Kawaguchi, Shogo*; Ohara, Koji*; et al.

Nature, 567(7749), p.506 - 510, 2019/03

 Times Cited Count:137 Percentile:99.28(Multidisciplinary Sciences)

Refrigeration is of vital importance for modern society for example, for food storage and air conditioning- and 25 to 30% of the world's electricity is consumed for refrigeration. Current refrigeration technology mostly involves the conventional vapour compression cycle, but the materials used in this technology are of growing environmental concern because of their large global warming potential. As a promising alternative, refrigeration technologies based on solid-state caloric effects have been attracting attention in recent decades. However, their application is restricted by the limited performance of current caloric materials, owing to small isothermal entropy changes and large driving magnetic fields. Here we report colossal barocaloric effects (CBCEs) (barocaloric effects are cooling effects of pressure-induced phase transitions) in a class of disordered solids called plastic crystals. The obtained entropy changes in a representative plastic crystal, neopentylglycol, are about 389 joules per kilogram per kelvin near room temperature. Pressure-dependent neutron scattering measurements reveal that CBCEs in plastic crystals can be attributed to the combination of extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of these materials. Our study establishes the microscopic mechanism of CBCEs in plastic crystals and paves the way to next-generation solid-state refrigeration technologies.

Journal Articles

Global continuous optimization with error bound and fast convergence

Kawaguchi, Kenji*; Maruyama, Yu; Zheng, X.

Journal of Artificial Intelligence Research, 56, p.153 - 195, 2016/06

 Times Cited Count:11 Percentile:56.6(Computer Science, Artificial Intelligence)

Journal Articles

Application of Bayesian nonparametric models to the uncertainty and sensitivity analysis of source term in a BWR severe accident

Zheng, X.; Ito, Hiroto; Kawaguchi, Kenji; Tamaki, Hitoshi; Maruyama, Yu

Reliability Engineering & System Safety, 138, p.253 - 262, 2015/06

 Times Cited Count:8 Percentile:41.1(Engineering, Industrial)

Journal Articles

Analysis for iodine release from Unit 3 of Fukushima Dai-ichi Nuclear Power Plant with consideration of water phase iodine chemistry

Ishikawa, Jun; Kawaguchi, Kenji; Maruyama, Yu

Journal of Nuclear Science and Technology, 52(3), p.308 - 314, 2015/03

 Times Cited Count:12 Percentile:72.88(Nuclear Science & Technology)

no abstracts in English

Journal Articles

An Adaptive time-stepping scheme with local convergence verification using support vector machines

Kawaguchi, Kenji; Ishikawa, Jun; Maruyama, Yu

International Journal of Engineering and Technology, 6(2), p.104 - 108, 2014/04

Journal Articles

Electro-deposition of tantalum on tungsten and nickel in LiF-NaF-CaF$$_{2}$$ melt containing K$$_{2}$$TaF$$_{7}$$; Electrochemical study

Mehmood, M.*; Kawaguchi, Nobuaki*; Maekawa, Hideki*; Sato, Yuzuru*; Yamamura, Tsutomu*; Kawai, Masayoshi*; Kikuchi, Kenji

Materials Transactions, 44(2), p.259 - 267, 2003/02

 Times Cited Count:8 Percentile:47.31(Materials Science, Multidisciplinary)

Electrochemical study has been carried out on the electro-deposition of tantalum in LiF-NaF-CaF$$_{2}$$ melt containing K$$_{2}$$TaF$$_{7}$$ at 700$$^{circ}$$C. This has been done for determining the mechanistic features for preparing electrolytic coating of tantalum on nickel and tungsten substrates. Electro-deposition of metallic tantalum occurs primarily by electro-reduction of Ta(V). Pure metallic tantalum without any entrapped salt is successfully deposited on tungsten by galvanostatic polarization at reasonably low current densities. An additional feature on nickel is the formation of an intermetallic compound at potential 0.25V nobler than that of pure tantalum as a result of underpotential deposition of tantalum. This intermetallic compound covers the surface within a short time followed by deposition of pure tantalum, although intermetallic compound keeps growing at the interface of pure tantalum deposit and the substrate as a result of diffusion.

Oral presentation

Radiation effects of the boron nano-belt on the electronic conductivity

Kirihara, Kazuhiro*; Kawaguchi, Kenji*; Shimizu, Yoshiki*; Sasaki, Takeshi*; Koshizaki, Naoto*; Kimura, Kaoru*; Yamada, Yoichi; Yamamoto, Hiroyuki; Shamoto, Shinichi

no journal, , 

Radiation effects of the boron nano-belt on the electronic conductivity have been studied.

Oral presentation

Radiation detection using boron nanobelts

Kirihara, Kazuhiro*; Kawaguchi, Kenji*; Shimizu, Yoshiki*; Sasaki, Takeshi*; Koshizaki, Naoto*; Kimura, Kaoru*; Yamada, Yoichi; Yamamoto, Hiroyuki; Shamoto, Shinichi

no journal, , 

We discuss the effects of neutron and $$gamma$$-ray irradiation on electrical transport of single-crystalline boron nanobelts toward a nano-scale radiation sensor device. Changes of electrical conductance of individual nanobelt before and after thermal neutron irradiation with low (10$$^{8}$$ cm$$^{-2}$$ s$$^{-1}$$) or high (3$$times$$10$$^{13}$$ cm$$^{-2}$$ s$$^{-1}$$) flux are presented.

Oral presentation

Effect of neutron irradiation on the electrical transport of boron nanobelt devices

Kirihara, Kazuhiro*; Kawaguchi, Kenji*; Shimizu, Yoshiki*; Sasaki, Takeshi*; Koshizaki, Naoto*; Kimura, Kaoru*; Yamada, Yoichi; Yamamoto, Hiroyuki; Shamoto, Shinichi

no journal, , 

Isotopic $$^{10}$$B atom has large thermal neutron capture cross section. $$^{7}$$Li atom and $$alpha$$ particle as a product of the neutron reaction can change the electrical transport property of the boron-rich semiconductor because they provide carrier doping and lattice defects. We successfully synthesized catalyst-free single-crystalline boron nanobelts (BNBs) and clarified the electrical transport and photoconduction mechanism of individual nanobelt. The BNB device is promising candidates for solid-state neutron sensors with both high resolution and good discrimination performance between neutron and $$gamma$$-ray. In the presentation, we discuss the performance of thermal neutron detection of BNB devices. Isotopic $$^{10}$$B enriched BNBs was synthesized to detect thermal neutrons efficiently. Electrical conductance of a nanobelt increased to eight times after the thermal neutron irradiation with a dose of 1.8$$times$$10$$^{14}$$ cm$$^{-2}$$ by the neutron reaction of $$^{10}$$B.

Oral presentation

Formation of Au and Pt nanoparticles on ion irradiated graphite substrates

Takahiro, Katsumi*; Morimoto, Keiichi*; Yasuda, Kenji*; Kawaguchi, Kazuhiro; Nagata, Shinji*; Yamamoto, Shunya; Narumi, Kazumasa; Naramoto, Hiroshi*

no journal, , 

no abstracts in English

Oral presentation

Study on microwave heating of Pu/U mixed nitrate medium in solid state on denitration process

Imai, Suguru*; Taguchi, Kenji*; Kashiwa, Tatsuya*; Kawaguchi, Koichi; Segawa, Tomomi

no journal, , 

In the nuclear cycle system, reprocessing solutions (plutonium and uranium mixed nitrate solution) produced from spent nuclear fuel is converted to Mixed Oxide (MOX) by a microwave heating (MH) method in Japan. The electric constant of the reprocessing solution is varied by its phase state on heating and denitration reaction and affects the microwave heating property. It is important to understand the property of the microwave heating for improving the efficiency. Therefore the temperature distribution of the solid state of the reprocessing solution is investigated by the electromagnetic analysis and thermal analysis using FDTD method and thermal analysis method. As a result, the absorbed power of the solid-state Pu-U mixed nitrate are concentrated at upper surface and periphery, and generated heat flows to below.

Oral presentation

Analytical study for release of gaseous iodine associated with containment venting operation

Ishikawa, Jun; Kawaguchi, Kenji; Maruyama, Yu

no journal, , 

no abstracts in English

Oral presentation

Evaluation on the denitration characteristics heated by the circular polarized microwave

Segawa, Tomomi; Tanigawa, Masafumi; Kato, Yoshiyuki; Kawaguchi, Koichi; Ishii, Katsunori; Suzuki, Masahiro; Kitazawa, Toshihide*; Taguchi, Kenji*; Kashiwa, Tatsuya*

no journal, , 

For the purpose of improving the microwave heating denitration technology, the denitration characteristics of cobalt nitrate aqueous solutions as a simulated materials were analyzed and evaluated by using the microwave heating equipment whichi was controlled to circular polarized wave. Numerical simulation confirmed that the circular polarized wave controlled microwave irradiation uniformed the absorbed power distribution in the circumferential direction. Moreover, it was confirmed that the denitration proceeded uniformly even in the radial direction by the microwave heating denitration experiments of cobalt nitrate aqueous solutions. From these results, it was revealed that favorable heating and denitration characteristics can be obtained by the circularly polarized wave controlled microwave heating equipment.

Oral presentation

Evaluation of the effects of granulated alumina powder characteristics and die wall lubricant on compaction behavior using X-ray computed tomography

Segawa, Tomomi; Kawaguchi, Koichi; Ishii, Katsunori; Nishina, Masahiro; Makino, Takayoshi; Iimura, Kenji*; Satone, Hiroshi*; Suzuki, Michitaka*; Natori, Yuri*

no journal, , 

Japan Atomic Energy Agency has developed a simplified pelletizing fuel fabrication system. In this system, the flowability of a MOX raw powder is improved by wet granulation for the pelletizing process, and the die wall lubrication method directly presses the granulated MOX powder into green pellets without adding any lubricant into the powder. The homogeneous compression is important to fabricate high-density green pellets. However, it is difficult to observe the compaction behavior in situ. Therefore, the capping phenomenon was investigated by using X-ray computed tomography and alumina powder that is highly transparent against X-rays. When lubricant was used, the breakage of the particles extended to the bottom compared with not used. This result indicates that the die wall lubrication is effective for the homogeneous compression of granulated powders.

14 (Records 1-14 displayed on this page)
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