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論文

Pressure-modulated magnetism and negative thermal expansion in the Ho$$_2$$Fe$$_{17}$$ intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; 加藤 健一*; 服部 高典; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

https://doi.org/10.1021/acs.chemmater.3c00158

静水圧や化学圧力は、結晶構造を変化させる効率的な刺激であり、材料科学において電気的、磁気的特性のチューニングによく利用されている。しかし、化学圧力は定量化が困難であり、これら両者の定量的な対応関係はまだよくわかっていない。本研究では、負の熱膨張(NTE)を持つ永久磁石の候補である金属間化合物を調べた。放射光X線その場観察により、AlをドープしたHo$$_2$$Fe$$_{17}$$に負の化学圧力があることを明らかにし、単位セル体積の温度・圧力依存性を用いそれを定量的に評価した。また、磁化測定と中性子回折測定を組み合わせることで、磁気秩序に対する化学圧力と静水圧の違いを比較した。興味深いことに、圧力はNTEの抑制と増強を制御するために使用することができた。電子状態計算から、圧力がFermiレベル(EF)に対する主要バンドの上部に影響を与えたことを示しており、これは磁気安定性に影響を与え、それが磁気とNTEを調節する上で重要な役割を果たしていることがわかった。本研究は、圧力の影響を理解し、それを利用して機能性材料の特性を制御する良い例を示している。

論文

Pore connectivity influences mass transport in natural rocks; Pore structure, gas diffusion and batch sorption studies

Yuan, X.*; Hu, Q.*; Lin, X.*; Zhao, C.*; Wang, Q.*; 舘 幸男; 深津 勇太; 濱本 昌一郎*; Siitari-Kauppi, M.*; Li, X.*

Journal of Hydrology, 618, p.129172_1 - 129172_15, 2023/03

https://doi.org/10.1016/j.jhydrol.2023.129172

Mass transport in geomedia as influenced by the pore structure is an important phenomenon. Six rocks (granodiorite, limestone, two chalks, mudstone, and dolostone) with different extents of heterogeneity at six different particle sizes were studied to describe the effects of pore connectivity on mass transport. The multiple methods applied were porosity measurement, gas diffusion test, and batch sorption test of multiple ions. Porosity measurement results reveal that with decreasing particle sizes, the effective porosities for the "heterogenous" group (granodiorite and limestone) increase, whereas the porosities of "homogeneous" group (chalks, mudstone, and dolostone) roughly remain constant. Gas diffusion results show that the intraparticle gas diffusion coefficient among these two groups, varying in the magnitude of 10$$^{-8}$$ to 10$$^{-6}$$ m$$^{2}$$/s. The batch sorption work displays a different affinity of these rocks for tracers, which are related to their mineral components. For granodiorite, mudstone, and dolostone, the adsorption capacity increases as the particle size decreases, due to higher specific surface area in smaller particle-size. In general, this integrated research of grain size distribution, rock porosity, intraparticle diffusivity, and ionic sorption capacity gives insights into the pore connectivity effect on both gas diffusion and chemical transport behaviors for different lithologies and/or different particle sizes.

論文

$$S$$-wave fully charmed tetraquark resonant states

Wang, G.-J.*; Meng, Q.*; 岡 眞

Physical Review D, 106(9), p.096005_1 - 096005_9, 2022/11

https://doi.org/10.1103/PhysRevD.106.096005

クォーク模型を用いて、チャームクォークの4体系であるテトラクォークのS波の共鳴状態の探索を行った。複素スケーリング法を用いた計算でスピンーパリティが$$J^{PC}=0^{++}$$, $$1^{+-}$$, $$2^{++}$$の各チャネルに2個ずつ共鳴が存在することを明らかにした。しかし、これらの共鳴は最近の実験で見つかった$$X(6900)$$と比べると100MeV近く高いところに存在していることが解った。

論文

Synergistic hybrid electrocatalysts of platinum alloy and single-atom platinum for an efficient and durable oxygen reduction reaction

Liu, B.*; Feng, R.*; Busch, M.*; Wang, S.*; Wu, H.*; Liu, P.*; Gu, J.*; Bahadoran, A.*; 松村 大樹; 辻 卓也; et al.

ACS Nano, 16(9), p.14121 - 14133, 2022/09

https://doi.org/10.1021/acsnano.2c04077
 被引用回数：9 パーセンタイル：84.81(Chemistry, Multidisciplinary)

Pt single-atom materials possess an ideal atom economy but suffer from limited intrinsic activity and side reaction of producing H$$_{2}$$O$$_{2}$$ in catalyzing the oxygen reduction reaction (ORR). Here, we demonstrate that anchoring platinum alloys on single-atom Pt-decorated carbon (Pt- SAC) surmounts their inherent deficiencies, thereby enabling a complete four-electron ORR pathway catalysis with high efficiency and durability. Pt$$_{3}$$Co@Pt-SAC demonstrates an exceptional mass and specific activities 1 order of magnitude higher than those of commercial Pt/C. They are durable throughout 50000 cycles, showing only a 10 mV decay in halfwave potential. The superior durability is attributed to the shielding effect of the Pt-SAC coating, which significantly mitigates the dissolution of Pt$$_{3}$$Co cores.

論文

Micro- to nano-scale areal heterogeneity in pore structure and mineral compositions of a sub-decimeter-sized Eagle Ford Shale

Wang, Q.*; Hu, Q.*; Zhao, C.*; Yang, X.*; Zhang, T.*; Ilavsky, J.*; Kuzmenko, I.*; Ma, B.*; 舘 幸男

International Journal of Coal Geology, 261, p.104093_1 - 104093_15, 2022/09

https://doi.org/10.1016/j.coal.2022.104093
 被引用回数：1 パーセンタイル：49.4(Energy & Fuels)

To understanding the spatial heterogeneity of mineral and pore structure variations in fine-grained shale, microscale X-ray fluorescence (micro-XRF) mapping, (ultra-) small-angle X-ray scattering [(U)SAXS] and wide-angle X-ray scattering were applied for two samples from a piece of Eagle Ford Shale in South Texas. Thin section petrography and field emission-scanning electron microscopy, X-ray diffraction (XRD), total organic carbon, and pyrolysis were also utilized to investigate the potential spatial heterogeneity of pore types, mineral and organic matter compositions for both samples. Overall, the siliceous-carbonate mineral contents in these carbonate-rich Eagle Ford Shale vary between laminations at mm scales. By analyzing six selected sub-samples on each of two samples with X-ray scattering and XRD techniques, nm-sized pores are mainly interparticle ones in the higher calcite regions, where the porosity is also relatively lower, while the lower calcite regions consist of both interparticle and intraparticle pore types with higher porosity. Finally, the micro-XRF and (U)SAXS are combined to generate porosity distribution maps to provide more insights about its heterogeneity related to the laminations and fractures at our observational scales.

論文

The $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross section from the surrogate ratio method and its effect on the $$^{60}$$Fe nucleosynthesis

Yan, S. Q.*; Li, X. Y.*; 西尾 勝久; Lugaro, M.*; Li, Z. H.*; 牧井 宏之; Pignatari, M.*; Wang, Y. B.*; Orlandi, R.; 廣瀬 健太郎; et al.

Astrophysical Journal, 919(2), p.84_1 - 84_7, 2021/10

https://doi.org/10.3847/1538-4357/ac12ce
 被引用回数：1 パーセンタイル：14.74(Astronomy & Astrophysics)

The long-lived $$^{60}$$Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe on $$^{59}$$Fe (half-life=44.5 days) is the key reaction for the production of $$^{60}$$Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 $$gamma$$-ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.5$$pm$$3.5 mb at $$kT$$ = 30 keV and 13.4$$pm$$1.7 mb at $$kT$$ = 90 keV, roughly 10%-20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of $$^{60}$$Fe from the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe rate are at most 25$$%$$. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of $$^{60}$$Fe.

論文

Origin of magnetovolume effect in a cobaltite

Miao, P.*; Tan, Z.*; Lee, S. H.*; 石川 喜久*; 鳥居 周輝*; 米村 雅雄*; 幸田 章宏*; 小松 一生*; 町田 真一*; 佐野 亜沙美; et al.

Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03

https://doi.org/10.1103/PhysRevB.103.094302
 被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)

層状ペロブスカイトPrBaCo$$_{2}$$O$$_{5.5}$$は、熱膨張のない複合材料を作るために必要な負の熱膨張(NTE)を示す。NTEは、自発的な磁気秩序と密接に関連していることがわかっていた(磁気体積効果: MVE)。今回、われわれは、PrBaCo$$_{2}$$O$$_{5.5}$$の連続的な磁気体積効果が、本質的には不連続であり、大きな体積を持つ反強磁性絶縁体(AFILV)から、小さな体積をもつ強磁性卑絶縁体(FLISV)への磁気電気的相転移に起因することを明らかにした。また、磁気電気効果(ME)は、温度,キャリアドーピング,静水圧,磁場などの複数の外部刺激に対して高い感度を示した。これは、これまでよく知られている対称性の破れを伴う巨大磁気抵抗やマルチフェロイック効果などのMEとは対照的であり、輝コバルト鉱のMEは同一の結晶構造で起こる。われわれの発見は、MEとNTEを実現するための新しい方法を示しており、それは新しい技術に応用されるかもしれない。

論文

Field-tuned magnetic structure and phase diagram of the honeycomb magnet YbCl$$_3$$

Hao, Y. Q.*; Wo, H. L.*; Gu, Y. M.*; Zhang, X. W.*; Gu, Y. Q.*; Zheng, S. Y.*; Zhao, Y.*; Xu, G. Y.*; Lynn, J. W.*; 中島 健次; et al.

Science China; Physics, Mechanics & Astronomy, 64(3), p.237411_1 - 237411_6, 2021/03

https://doi.org/10.1007/s11433-020-1626-3
 被引用回数：3 パーセンタイル：42.28(Physics, Multidisciplinary)

We report thermodynamic and neutron diffraction measurements on the magnetic ordering properties of the honeycomb lattice magnet YbCl$$_3$$. We find YbCl$$_3$$ exhibits a N${'e}$el type long-range magnetic order at the wavevector (0, 0, 0) below T$$_N$$ = 600 mK. This magnetic order is associated with a small sharp peak in heat capacity and most magnetic entropy release occurs above the magnetic ordering temperature. The magnetic moment lies in-plane, parallel to the monoclinic a-axis, whose magnitude m$$_{rm Yb}$$ = 0.86(3) $$mu_B$$ is considerably smaller than the expected fully ordered moment of 2.24 $$mu_B$$ for the doublet crystal-field ground state. The magnetic ordering moment gradually increases with increasing magnetic field perpendicular to the ab-plane, reaching a maximum value of 1.6(2) $$mu_B$$ at 4 T, before it is completely suppressed above $$sim$$9 T. These results indicate the presence of strong quantum fluctuations in YbCl$$_3$$.

論文

Coordination number regulation of molybdenum single-atom nanozyme peroxidase-like specificity

Wang, Y.*; Jia, G.*; Cui, X.*; Zhao, X.*; Zhang, Q.*; Gu, L.*; Zheng, L.*; Li, L. H.*; Wu, Q.*; Singh, D. J.*; et al.

Chem, 7(2), p.436 - 449, 2021/02

https://doi.org/10.1016/j.chempr.2020.10.023
 被引用回数：115 パーセンタイル：99.78(Chemistry, Multidisciplinary)

Nanozymes are promising alternatives to natural enzymes, but their use remains limited owing to poor specificity. Overcoming this is extremely challenging due to the intrinsic structural complexity of these systems. We report theoretical design and experimental realization of a series of heterogeneous molybdenum single-atom nanozymes (named Mo$$_{rm{SA}}$$-N$$_{x}$$-C), wherein we find that the peroxidase-like specificity is well regulated by the coordination numbers of single Mo sites. The resulting Mo$$_{rm{SA}}$$-N$$_{3}$$-C catalyst shows exclusive peroxidase-like behavior. It achieves this behavior via a homolytic pathway, whereas Mo$$_{rm{SA}}$$-N$$_{2}$$-C and Mo$$_{rm{SA}}$$-N$$_{4}$$-C catalysts have a different heterolytic pathway. The mechanism of this coordination-number-dependent enzymatic specificity is attributed to geometrical structure differences and orientation relationships of the frontier molecular orbitals.

論文

General synthesis of single-atom catalysts for hydrogen evolution reactions and room-temperature Na-S batteries

Lai, W.-H.*; Wang, H.*; Zheng, L.*; Jiang, Q.*; Yan, Z.-C.*; Wang, L.*; 吉川 浩史*; 松村 大樹; Sun, Q.*; Wang, Y.-X.*; et al.

Angewandte Chemie; International Edition, 59(49), p.22171 - 22178, 2020/12

https://doi.org/10.1002/anie.202009400
 被引用回数：58 パーセンタイル：95.97(Chemistry, Multidisciplinary)

Herein, we report a comprehensive strategy to synthesize a full range of single-atom metals on carbon matrix, including V, Mn, Fe, Co, Ni, Cu, Ge, Mo, Ru, Rh, Pd, Ag, In, Sn, W, Ir, Pt, Pb, and Bi. The extensive applications of various single-atom catalysts (SACs) are manifested via their ability to electro-catalyze typical hydrogen evolution reactions (HER) and conversion reactions in novel room-temperature sodium sulfur batteries (RT-Na-S). The enhanced performances for these electrochemical reactions arisen from the ability of different single active atoms on local structures to tune their electronic configuration. Significantly, the electrocatalytic behaviors of diverse SACs, assisted by density functional theory calculations, are systematically revealed by in situ synchrotron X-ray diffraction and in situ transmission electronic microscopy, providing a strategic library for the general synthesis and extensive applications of SACs in energy conversion and storage.

論文

Fine structure in the $$alpha$$ decay of $$^{223}$$U

Sun, M. D.*; Liu, Z.*; Huang, T. H.*; Zhang, W. Q.*; Andreyev, A. N.; Ding, B.*; Wang, J. G.*; Liu, X. Y.*; Lu, H. Y.*; Hou, D. S.*; et al.

Physics Letters B, 800, p.135096_1 - 135096_5, 2020/01

https://doi.org/10.1016/j.physletb.2019.135096
 被引用回数：9 パーセンタイル：81.58(Astronomy & Astrophysics)

Fine structure in the $$alpha$$ decay of $$^{223}$$U was observed in the fusion-evaporation reaction $$^{187}$$Re($$^{40}$$Ar,p3n) by using fast digital pulse processing technique. Two $$alpha$$-decay branches of $$^{223}$$U feeding the ground state and 244 keV excited state of $$^{219}$$Th were identified by establishing the decay chain $$^{223}$$U$$rightarrow$$$$^{219}$$Th$$rightarrow$$$$^{215}$$Ra$$rightarrow$$$$^{211}$$Rn. The $$alpha$$-particle energy for the ground-state to ground-state transition of $$^{223}$$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62$$^{+14}_{-10} mu$$s. Evolution of nuclear structure for $$N$$=131 even-$$Z$$ isotones from Po to U was discussed in the frameworks of nuclear mass and reduced $$alpha$$-decay width, a weakening octupole deformation in the ground state of $$^{223}$$U relative to its lighter isotones $$^{219}$$Ra and $$^{211}$$Th was suggested.

論文

Comparison of heavy-ion transport simulations; Collision integral with pions and $$Delta$$ resonances in a box

小野 章*; Xu, J.*; Colonna, M.*; Danielewicz, P.*; Ko, C. M.*; Tsang, M. B.*; Wang, Y,-J.*; Wolter, H.*; Zhang, Y.-X.*; Chen, L.-W.*; et al.

Physical Review C, 100(4), p.044617_1 - 044617_35, 2019/10

AA2019-0025.pdf:2.76MB

https://doi.org/10.1103/PhysRevC.100.044617
 被引用回数：48 パーセンタイル：98.64(Physics, Nuclear)

2017年4月に開催された国際会議Transport2017において、重イオン核反応モデルの国際的な比較が議論された。重イオン加速器の安全評価や宇宙飛行士の被ばく評価等で重要な役割を果たすため、世界中で重イオン核反応の様々な理論モデルが開発されている。本研究では、辺の長さが20fmの直方体に320個の中性子と陽子をランダム配置し、それらが70fm/cの間に起こす散乱の回数やエネルギーを計算した。ここでは、特にパイオンやその前駆体であるデルタ共鳴の生成に注目して比較を行った。参加コードは、個々の粒子の時間発展を追うQMD型コードと、粒子の位置や運動量の確率分布を決めておき、散乱や崩壊が発生したときそれらを乱数サンプリングするBUU型コードがあり、発表者が用いたJQMDは前者に属する。本研究により、計算における時間刻みが各コードによる結果の差の主な原因であることが分かった。さらに、今後のJQMDの改良方針の策定に有益な知見を得ることができた。

論文

Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe$$_{2}$$Ge$$_{2}$$

Wo, H.*; Wang, Q.*; Shen, Y.*; Zhang, X.*; Hao, Y.*; Feng, Y.*; Shen, S.*; He, Z.*; Pan, B.*; Wang, W.*; et al.

Physical Review Letters, 122(21), p.217003_1 - 217003_5, 2019/05

https://doi.org/10.1103/PhysRevLett.122.217003
 被引用回数：3 パーセンタイル：33.85(Physics, Multidisciplinary)

We report neutron scattering measurements of single-crystalline YFe$$_{2}$$Ge$$_{2}$$ in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFe$$_{2}$$Ge$$_{2}$$ does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFe$$_{2}$$Ge$$_{2}$$ displays anisotropic stripe-type antiferromagnetic spin fluctuations at ($$pi, 0, pi$$). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector ($$0, 0, pi$$). These ferromagnetic spin fluctuations are isotropic in the ($$H, K$$) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe$$_{2}$$Ge$$_{2}$$ and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.

論文

Asymmetrically optimized structure in a high-$$T_{rm c}$$ single unit-cell FeSe superconductor

深谷 有喜; Zhou, G.*; Zheng, F.*; Zhang, P.*; Wang, L.*; Xue, Q.-K.*; 社本 真一

Journal of Physics; Condensed Matter, 31(5), p.055701_1 - 055701_6, 2019/02

https://doi.org/10.1088/1361-648X/aaf2d9
 被引用回数：4 パーセンタイル：26.49(Physics, Condensed Matter)

本研究では、SrTiO$$_{3}$$基板上の単層FeSeの構造が上下方向に非対称化していることを報告する。SrTiO$$_{3}$$基板上の単層FeSeは、鉄系超伝導体において最も高い転移温度(50K以上)を示す。全反射高速陽電子回折(TRHEPD)を用いた構造解析の結果、真空側と界面側のSe-Fe層間隔は異なり、上下方向に非対称な構造であることがわかった。これらの層間隔および結合角の平均値は、圧力下のバルクFeSeにおいて高い転移温度を示す最適値と一致している。したがって、SrTiO$$_{3}$$基板上の単層FeSeは非対称化することにより高い転移温度を発現するための最適構造を形成したと考えられる。

論文

Liquid-like thermal conduction in intercalated layered crystalline solids

Li, B.; Wang, H.*; 川北 至信; Zhang, Q.*; Feygenson, M.*; Yu, H. L.*; Wu, D.*; 尾原 幸治*; 菊地 龍弥*; 柴田 薫; et al.

Nature Materials, 17(3), p.226 - 230, 2018/03

https://doi.org/10.1038/s41563-017-0004-2
 被引用回数：98 パーセンタイル：96.59(Chemistry, Physical)

As a generic property, all substances transfer heat through microscopic collisions of constituent particles. A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations. As a result, a solid is usually thermally more conductive than a liquid. In canonical viewpoints, such a difference also serves as the dynamic signature distinguishing a solid from a liquid. Here, we report liquid-like thermal conduction observed in the crystalline AgCrSe$$_{2}$$. The transverse acoustic phonons are completely suppressed by the ultrafast dynamic disorder while the longitudinal acoustic phonons are strongly scattered but survive, and are thus responsible for the intrinsically ultralow thermal conductivity. This scenario is applicable to a wide variety of layered compounds with heavy intercalants in the van der Waals gaps, manifesting a broad implication on suppressing thermal conduction. These microscopic insights might reshape the fundamental understanding on thermal transport properties of matter and open up a general opportunity to optimize performances of thermoelectrics.

論文

Comparison of heavy-ion transport simulations; Collision integral in a box

Zhang, Y.-X.*; Wang, Y,-J.*; Colonna, M.*; Danielewicz, P.*; 小野 章*; Tsang, M. B.*; Wolter, H.*; Xu, J.*; Chen, L.-W.*; Cozma, D.*; et al.

Physical Review C, 97(3), p.034625_1 - 034625_20, 2018/03

https://doi.org/10.1103/PhysRevC.97.034625
 被引用回数：85 パーセンタイル：99.25(Physics, Nuclear)

2017年4月に開催された国際会議Transport2017において、重イオン核反応モデルの国際的な比較が議論された。重イオン加速器の安全評価や宇宙飛行士の被ばく評価等で重要な役割を果たすため、世界中で重イオン核反応の様々な理論モデルが開発されている。本研究はモデル間の共通点と差異を明らかにし、各モデルの問題点を明らかにした。比較において、辺の長さが20fmの直方体に320個の中性子と320個の陽子をランダム配置し、それらが時間発展に伴って起こす散乱の回数や散乱時のエネルギーなどを計算する条件が設定された。また、結果以外にも、理論モデルを構成するアルゴリズムについても比較を行った。発表者は重イオン核反応モデルJQMD(JAERI Quantum Molecular Dynamics)を用いて計算を行い、世界で開発されている15の計算コードによる計算結果と比較した。コードアルゴリズムの比較では、JQMDは必ず陽子から 優先的に衝突確率を計算し、その後に中性子の衝突を計算するため、物理描像の妥当性が指摘された。一方、JQMDは他のモデルとほぼ同じ計算結果を出すことも判明した。衝突回数や運動量の計算値が平均から2倍以上乖離するモデルもある中で、JQMDは本計算条件で安定した性能を発揮することが確認された。

論文

The $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr cross section from the surrogate ratio method and its effect on $$s$$-process nucleosynthesis

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; 西尾 勝久; Lugaro, M.*; Karakas, A. I.*; 牧井 宏之; Mohr, P.*; Su, J.*; Li, Y. J.*; et al.

Astrophysical Journal, 848(2), p.98_1 - 98_8, 2017/10

https://doi.org/10.3847/1538-4357/aa8c74
 被引用回数：5 パーセンタイル：23.68(Astronomy & Astrophysics)

The $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr reaction cross section is crucial in the modelling of $$s$$-process nucleosynthesis in asymptotic giant branch stars because it controls the operation of the branching point at the unstable $$^{95}$$Zr and the subsequent production of $$^{96}$$Zr. We have carried out the measurement of the $$^{90}$$Zr($$^{18}$$O,$$^{16}$$O) and $$^{94}$$Zr($$^{18}$$O,$$^{16}$$O) reactions and obtained the $$gamma$$-decay probability ratio of $$^{92}$$Zr$$^{*}$$ and $$^{96}$$Zr$$^{*}$$ to determine the $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr reaction cross sections with the surrogate ratio method. We tested our deduced maxwellian-averaged cross section in stellar models with masses between 2 and 6 $$M_{odot}$$ and metallicities 0.014 and 0.03. The largest changes - up 80 % variations in $$^{96}$$Zr - are seen in the models of 3-4 $$M_{odot}$$, where the $$^{22}$$Ne neutron source is mildly activated. The new rate can still provide a match to data from meteoritic stardust silicon carbide grains, provided the maximum mass of the parent stars is below 4 $$M_{odot}$$, for a metallicity of 0.03.

論文

Effect of storage environment on hydrogen generation by the reaction of Al with water

Wang, Y.-Q.*; Gai, W.-Z.*; Zhang, X.-Y.*; Pan, H.-Y.*; Cheng, Z.-X.*; 徐 平光; Deng, Z.-Y.*

RSC Advances (Internet), 7(4), p.2103 - 2109, 2017/01

AA2016-0521.pdf:1.55MB

https://doi.org/10.1039/C6RA25563A
 被引用回数：23 パーセンタイル：65.19(Chemistry, Multidisciplinary)

Al powder was stored in saturated water vapor, oxygen, nitrogen and drying air separately for a time period up to about six months, the degradation behavior of Al activity was characterized by the reaction of Al with water. It was found that water vapor decreased the induction time for the beginning of Al-water reaction and reduced the total hydrogen generation per unit weight of Al, while oxygen increased the induction time and retarded the Al-water reaction. In contrast, the effect of nitrogen and drying air on Al activity was weak. The mechanism analyses indicated that water vapor promoted the hydration of Al surface passive oxide film and speeded up the reaction of Al with water, while oxygen thickened the passive oxide film of Al surface and prolonged its hydration process. These imply that water vapor rather than oxygen is responsible for the degradation of Al activity during storage under ambient condition.

論文

Examination of the surrogate ratio method for the determination of the $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr cross section with $$^{90,92}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{92,94}$$Zr reactions

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; 西尾 勝久; 牧井 宏之; Su, J.*; Li, Y. J.*; 西中 一朗; 廣瀬 健太郎; Han, Y. L.*; et al.

Physical Review C, 94(1), p.015804_1 - 015804_5, 2016/07

https://doi.org/10.1103/PhysRevC.94.015804
 被引用回数：6 パーセンタイル：46.78(Physics, Nuclear)

The relative $$gamma$$-decay probability ratios of the neutron resonance states in $$^{94}$$Zr and $$^{92}$$Zr populated via two neutron transfer reactions, $$^{92}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{94}$$Zr and $$^{90}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{92}$$Zr, have been measured to test the validity of the surrogate ratio method (SRM) in determining the (n,$$gamma$$) reaction cross section. The cross sections of the $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr reaction are derived from the experimentally obtained ratios and the cross sections of the $$^{91}$$Zr(n,$$gamma$$)$$^{92}$$Zr reaction in the equivalent neutron energy range of $$E_{rm n}$$ = 0 - 8 MeV. The deduced cross sections of $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr reaction agree with the directly measured ones in the low-energy region, and with the evaluated ENDF/B-VII.1 data at higher energies of $$E_{rm n} >$$ 3 MeV. The agreement supports the concept of the SRM method to indirectly determine the (n,$$gamma$$) reaction cross sections.

論文

Colossal negative thermal expansion induced by magnetic phase competition on frustrated lattices in Laves phase compound (Hf,Ta)Fe$$_2$$

Li, B.; Luo, X. H.*; Wang, H.*; Ren, W. J.*; Yano, S.*; Wang, C.-W.*; Gardner, J. S.*; Liss, K.-D.*; Miao, P.*; Lee, S.-H.*; et al.

Physical Review B, 93(22), p.224405_1 - 224405_6, 2016/06

https://doi.org/10.1103/PhysRevB.93.224405
 被引用回数：40 パーセンタイル：84.69(Materials Science, Multidisciplinary)

Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf$$_{0.86}$$Ta$$_{0.14}$$Fe$$_2$$ is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120$$^{circ}$$ frustrated antiferromagnetic state with well-reduced magnetic moment and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, $$-123 times 10^{-6}$$/K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few Tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.

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