Short-range spin order in paramagnetic AgCrSe

Nakamura, Jumpei*; Kawakita, Yukinobu; Okabe, Hirotaka*; Li, B.*; Shimomura, Koichiro*; Suemasu, Takashi*

Journal of Physics and Chemistry of Solids, 175, p.111199_1 - 111199_8, 2023/04

https://doi.org/10.1016/j.jpcs.2022.111199

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Retreat from stress; Rattling in a planar coordination

Suekuni, Koichiro*; Lee, C. H.*; Tanaka, Hiromi*; Nishibori, Eiji*; Nakamura, Atsushi*; Kasai, Hidetaka*; Mori, Hitoshi*; Usui, Hidetomo*; Ochi, Masayuki*; Hasegawa, Takumi*; et al.

Advanced Materials, 30(13), p.1706230_1 - 1706230_6, 2018/03

https://doi.org/10.1002/adma.201706230

Thermoelectric materials for highly efficient devices must satisfy conflicting requirements of high electrical conductivity and low thermal conductivity. In this paper, we studied the crystal structure and phonon dynamics of tetrahedrites (Cu,Zn)(Sb,As)S. The results revealed that the Cu atoms in a planar coordination are rattling, which effectively scatter phonons. These findings provide a new strategy for the development of highly efficient thermoelectric materials with planar coordination.

Radial density distribution in irradiated FBR MOX fuel pellets

Ishimi, Akihiro; Katsuyama, Kozo; Nakamura, Hirofumi; Asaka, Takeo; Furuya, Hirotaka

Nuclear Technology, 189(3), p.312 - 317, 2015/03

https://doi.org/10.13182/NT14-34

A high resolution X-ray CT technique was developed, which made it possible to obtain fine X-ray CT images of an irradiated fuel assembly. In addition, the density distributions in the irradiated MOX fuel pellet could be continually measured, using the relationship between the densities and CT values. These results were compared to the one obtained by metallographical method. As results, it was found that the relative change of radial density distributions in the irradiated fuel pellet can be measured more accurately by the X-ray CT technique than by the metallographical examination.

Positive-negative dual-tone sensitivities of ZEP resist

Oyama, Tomoko; Nakamura, Hirotaka*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*

Applied Physics Express, 7(3), p.036501_1 - 036501_3, 2014/03

https://doi.org/10.7567/APEX.7.036501

A chlorinated polymer ZEP is a main-chain scission type (positive-tone) high-sensitivity resist. However, we found that ZEP changes to negative-tone with a high dose of electron beam irradiation. The sensitivities to a 100 kV electron beam as a dual-tone are evaluated with various developers. Owing to different solvation strengths, the resist sensitivity varied with different developers in the positive-tone region. On the other hand, it was found that the threshold dose for the positive-negative inversion is independent of the developer. According to an analysis using X-ray photoelectron spectroscopy and NMR spectroscopy, we found that the amount of chlorine atoms and terminal double bonds generated by chain scission determines the threshold of the P-N inversion. This result provides important information for possible ZEP applications such as a dual-tone resist.

A Simple approach to the prediction of transient self-leveling behavior of debris bed

Cheng, S.*; Kai, Takayuki*; Gondai, Yoji*; Nakamura, Yuya*; Fuke, Fusata*; Zhang, B.*; Matsumoto, Tatsuya*; Morita, Koji*; Yamano, Hidemasa; Tagami, Hirotaka; et al.

Proceedings of 4th International Symposium on Heat Transfer and Energy Conservation (CD-ROM), 5 Pages, 2012/01

Model experiment of cosmic ray acceleration due to an incoherent wakefield induced by an intense laser pulse

Kuramitsu, Yasuhiro*; Nakanii, Nobuhiko*; Kondo, Kiminori; Sakawa, Yoichi*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; et al.

Physics of Plasmas, 18(1), p.010701_1 - 010701_4, 2011/01

https://doi.org/10.1063/1.3528434

Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma. An intensive laser pulse was propagated in a plasma tube created by imploding a hollow polystyrene cylinder, as the large amplitude light waves propagated in the upstream plasma at an astrophysical shock. Nonthermal electrons were generated, and the energy distribution functions of the electrons have a power-law component with an index of 2.

Correlation between laser accelerated MeV proton and electron beams using simple fluid model for target normal sheath acceleration

Tampo, Motonobu; Awano, Shinya*; Bolton, P.; Kondo, Kiminori; Mima, Kunioki*; Mori, Yoshitaka*; Nakamura, Hirotaka*; Nakatsutsumi, Motoaki*; Stephens, R. B.*; Tanaka, Kazuo*; et al.

Physics of Plasmas, 17(7), p.073110_1 - 073110_5, 2010/07

https://doi.org/10.1063/1.3459063

Superthermal and efficient-heating modes in the interaction of a cone target with ultraintense laser light

Nakamura, Hirotaka*; Chrisman, B.*; Tanimoto, Tsuyoshi*; Borghesi, M.*; Kondo, Kiminori; Nakatsutsumi, Motoaki*; Norimatsu, Takayoshi*; Tampo, Motonobu; Tanaka, Kazuo*; Yabuuchi, Toshinori*; et al.

Physical Review Letters, 102(4), p.045009_1 - 045009_4, 2009/01

https://doi.org/10.1103/PhysRevLett.102.045009

Interactions between a relativistic-intensity laser pulse and a cone-wire target are studied by changing the focusing point of the pulse. The pulse, when focused on the sidewall of the cone, produced superthermal electrons with an energy 10 MeV, whereas less energetic electrons 1 MeV were produced by the pulse when focused on the cone tip. Efficient heating of the wire was indicated by significant neutron signals observed when the pulse was focused on the tip. Particle-in-cell simulation results show reduced heating of the wire due to energetic electrons produced by specularly reflected light at the sidewall.

Fast heating of cylindrically imploded plasmas by petawatt laser light

Nakamura, Hirotaka*; Sentoku, Yasuhiko*; Matsuoka, Takeshi*; Kondo, Kiminori; Nakatsutsumi, Motoaki*; Norimatsu, Takayoshi*; Shiraga, Hiroyuki*; Tanaka, Kazuo*; Kodama, Ryosuke*

Physical Review Letters, 100(16), p.165001_1 - 165001_4, 2008/04

https://doi.org/10.1103/PhysRevLett.100.165001

We produced cylindrically imploded plasmas, which have the same density-radius product of the imploded plasma R with the compressed core in the fast ignition experiment and demonstrated efficient fast heating of cylindrically imploded plasmas with an ultraintense laser light. The coupling efficiency from the laser to the imploded column was 14%-21%, implying strong collimation of energetic electrons over a distance of 300 micron of the plasma. Particle-in-cell simulation shows confinement of the energetic electrons by self-generated magnetic and electrostatic fields excited along the imploded plasmas, and the efficient fast heating in the compressed region.