Progressive release of long-stored carbon from tropical peatland disturbances

小嵐 淳; 伊藤 雅之*; 安藤 麻里子; 國分 陽子; 松枝 誠; Kusin, K.*; Jaya, A.*; Dohong, S.*; 平野 高司*

Nature Communications (Internet), 17, p.4369_1 - 4369_9, 2026/05

https://doi.org/10.1038/s41467-026-72890-y

熱帯泥炭地は重要かつ長期的な炭素貯蔵庫であるが、人間活動によって劣化が進み、大気への炭素放出が深刻な懸念となっている。本研究は、インドネシア中部カリマンタンの泥炭地における炭素貯留と放出について、泥炭層と地下水溶存有機炭素の放射性炭素年代測定に基づいて明らかにした。18年間(1996年2014年)の排水は、数百年から千年もの間、浸水環境で保存されていた炭素5-11kg C mを放出した。排水に続く火災は、過去3000年間に蓄積された炭素23-32kg C mを放出し、より古い泥炭の分解を誘発した。この知見をインドネシアの撹乱された泥炭地全域に外挿すると、1996年から2014年の間に0.81-3.70Gtの炭素が放出されたことが示唆された。さらに継続的な泥炭の分解によって年間0.03-0.08Gtの炭素が放出され続けており、地球の炭素収支に重大な影響を及ぼしている。

TiC nanoparticles tune phase stability and deformation mechanisms in directed energy deposition processed Fe60Co15Ni15Cr10 medium-entropy alloy composites

Ahn, S. Y.*; Kim, E. S.*; Jeong, S. G.*; Harjo, S.; 川崎 卓郎; Gong, W.; Kim, H.-J.*; Hong, S.-J.*; Hong, S. I.*; Kwon, H.*; et al.

Materials Science & Engineering A, 955, p.149839_1 - 149839_18, 2026/03

https://doi.org/10.1016/j.msea.2026.149839

Additive manufacturing (AM) of particle-reinforced metal matrix composites (MMCs) enables control of both strength and deformation behavior. In this study, TiC (2 wt%) nanoparticles were added to FeCoNiCr medium-entropy alloy (MEA) using directed energy deposition (DED). Although part of the TiC decomposed during processing, the released C and Ti stabilized the -austenite phase and suppressed deformation-induced martensitic transformation (DIMT), shifting deformation toward slip-dominated behavior. Microstructural observations revealed dispersed TiC particles and modified grain boundary morphology that promoted distributed plastic flow. In-situ neutron diffraction during tensile testing confirmed enhanced early-stage dislocation activity. These findings demonstrate that nanoparticle-induced phase stability changes strongly influence deformation mechanisms in AM-processed MMCs.

Fundamental mechanisms of discontinuous deformation in metals for cryogenic-environment applications

Kim, Y. S.*; Kang, T.*; Hong, S.-K.*; Brechtl, J.*; Lebyodkin, M.*; Cheng, Y.-H.*; Huang, E.-W.*; Liaw, P. K.*; Harjo, S.; Gong, W.; et al.

Acta Materialia, 292, p.120970_1 - 120970_16, 2025/06

https://doi.org/10.1016/j.actamat.2025.120970

Metallic materials can exhibit low-temperature serrated deformation (LTSD) at cryogenic temperatures, potentially causing sudden failures. Understanding LTSD is thus crucial for ensuring material reliability in such environments. LTSD has been explained by two main mechanisms: (i) dislocation-based mechanical instability and (ii) thermomechanical instability, but each has limitations when considered alone. To address this, we propose a new LTSD mechanism, a thermally induced dislocation dynamics model, based on cryogenic experimental evidence. This model accounts for dislocation avalanches and localized heating, leading to hierarchical dislocation networks and transitions in deformation modes. A modified deformation-mechanism map for SS316L is also presented. Our findings highlight the rate-dependent nature of LTSD and negative strain-rate sensitivity, including the first observation of links between small stress fluctuations and large serrations.

Direct observations of dynamic and reverse transformation of Ti-6Al-4V alloy and pure titanium

Guo, B.*; Chen, H.*; Chong, Y.*; Mao, W.; Harjo, S.; Gong, W.; Zhang, Z.*; Jonas, J. J.*; 辻 伸泰*

Acta Materialia, 268, p.119780_1 - 119780_11, 2024/04

https://doi.org/10.1016/j.actamat.2024.119780

This paper focused on the characterization and mechanism of the dynamic transformation from the alpha to beta phase during the hot deformation of Ti-6Al-4V alloy and pure titanium. The investigation employed in-situ neutron diffraction and atomistic simulations for a comprehensive understanding of the process. Dynamic transformations were observed during deformation of the Ti-6Al-4V alloy and pure titanium below the beta transus temperatures. During isothermal holding after unloading, the in-situ neutron diffraction results for Ti-6Al-4V and pure titanium indicated a sluggish reverse transformation from the beta to alpha phase. The mechanism of dynamic transformation was explored through in-situ neutron diffraction and atomistic simulations, which revealed twofold effects of deformation on dynamic transformation. Firstly, deformation led to a significant rise in the Gibbs energy of the alpha phase relative to the beta phase, expanding the beta phase region and diminishing the alpha phase region. Secondly, deformation lowered the energy barriers associated with dynamic transformation, facilitating the activation of dynamic transformation more readily than in the equilibrium state before deformation.

Microstructural evolution and mechanical properties of non-equiatomic (CoNi)CrFeC high-entropy alloy

Kim, Y. S.*; Chae, H.*; Huang, E.-W.*; Jain, J.*; Harjo, S.; 川崎 卓郎; Hong, S. I.*; Lee, S. Y.*

Materials, 15(4), p.1312_1 - 1312_11, 2022/02

https://doi.org/10.3390/ma15041312

In this study, we manufactured a non-equiatomic (CoNi)CrFeC high-entropy alloy (HEA) consisting of a single-phase face-centered-cubic structure. The non-equiatomic (CoNi)CrFeC HEA revealed a good combination of strength and ductility in mechanical properties compared to the equiatomic CoNiCrFe HEA, due to both stable solid solution and precipitation-strengthened effects. The non-equiatomic stoichiometry resulted in not only a lower electronegativity mismatch, indicating a more stable state of solid solution, but also a higher stacking fault energy (SFE, 50 mJ/m) due to the higher amount of Ni and the lower amount of Cr. This higher SFE led to a more active motion of dislocations relative to mechanical twinning, resulting in severe lattice distortion near the grain boundaries and dislocation entanglement near the twin boundaries.

J/ near

Song, T.*; Gubler, P.; Hong, J.*; Lee, S. H.*; 森田 健司*

Physics Letters B, 813, p.136065_1 - 136065_5, 2021/02

https://doi.org/10.1016/j.physletb.2021.136065

We calculate the mass shift and thermal decay width of the J/ near the QCD transition temperature by imposing two independent constraints on these variables that can be obtained first by solving the Schrodinger equation and second from the QCD sum rule approach. While the real part of the potential is determined by comparing the QCD sum rule result for charmonium and the D meson to that from the potential model result, the imaginary potential is taken to be proportional to the perturbative form multiplied by a constant factor, which in turn can be determined by applying the two independent constraints. The result shows that the binding energy and the thermal width becomes similar in magnitude at around T = 1.09 , above which the sum rule analysis also becomes unstable, strongly suggesting that the J/ will melt slightly above .

Signatures of the vortical quark-gluon plasma in hadron yields

田屋 英俊*; Park, A.*; Cho, S.*; Gubler, P.; 服部 恒一*; Hong, J.*; Huang, X.-G.*; Lee, S. H.*; 門内 明彦*; 大西 明*; et al.

Physical Review C, 102(2), p.021901_1 - 021901_6, 2020/08

AA2020-0306.pdf:0.47MB

https://doi.org/10.1103/PhysRevC.102.021901

We investigate the hadron production from the vortical quark-gluon plasma created in heavy-ion collisions. Based on the quark-coalescence and statistical hadronization models, we show that total hadron yields summed over the spin components are enhanced by the local vorticity with quadratic dependence. The enhancement factor amounts to be a few percent and may be detectable within current experimental sensitivities. We also show that the effect is stronger for hadrons with larger spin, and thus propose a new signature of the local vorticity, which may be detected by the yield ratio of distinct hadron species having different spins such as and . The vorticity dependence of hadron yields seems robust, with consistent predictions in both of the hadron production mechanisms for reasonable values of the vorticity strength estimated for heavy-ion collisions.

-electron states in PrPdAl

目時 直人; 山内 宏樹; 鈴木 博之*; 北澤 英明*; 萩原 雅人*; 益田 隆嗣*; Aczel, A. A.*; Chi, S.*; Hong, T.*; 松田 雅昌*; et al.

Journal of the Physical Society of Japan, 87(9), p.094704_1 - 094704_8, 2018/09

https://doi.org/10.7566/JPSJ.87.094704

中性子非弾性散乱実験によりPrPdAlの電子状態を明らかにした。この物質のユニークな結晶構造に起因する2次元的な結晶場ポテンシャルにより、大きなを伴う平べったい軌道が安定化し、イジング型の磁気異方性が生じることがわかった。この2次元的な結晶場ポテンシャルは同じ結晶構造を持つ希土類化合物RPdAlに共通に存在し、重い電子系超伝導体NpPdAlにおけるXY型磁気異方性への変化を系統的に説明することができる。それは、電子の局所的な性質がこの物質系の物性発現機構において非常に重要であり、NpPdAlにおける重い電子系超伝導にも関与している。

Accuracy of prediction method of cryogenic tensile strength for austenitic stainless steels in ITER toroidal field coil structure

櫻井 武尊; 井口 将秀; 中平 昌隆; 斎藤 徹*; 森本 将明*; 稲垣 隆*; Hong, Y.-S.*; 松井 邦浩; 辺見 努; 梶谷 秀樹; et al.

Physics Procedia, 67, p.536 - 542, 2015/07

https://doi.org/10.1016/j.phpro.2015.06.072

原子力機構はこれまで、極低温で使用されるITER超伝導コイルに適用するオーステナイト系ステンレス鋼の合理的な品質管理手法の開発確立を目的に、室温で測定された引張強さと、炭素と窒素の含有量の関数として二次曲線を用いた4Kでの引張強度予測手法を開発してきた。核融合発電の技術的成立の実証を目指して建設が進んでいるITERでは、超伝導コイルが使用される。超伝導コイルシステムの一つであるTFコイルの容器構造物には巨大な電磁力に耐えるため、構造材料として高マンガンステンレス鋼JJ1及び高窒素添加型316LNが使用される。原子力機構はITER TFコイル構造物の調達責任を負っており、2012年から実機構造材料調達を開始し、矩形材,丸棒材,異形鍛造材などの製造を進めている。原子力機構は、構造材料の高マンガンステンレス鋼JJ1及び高窒素添加型316LNの機械特性を多数取得しており、本研究ではこれらの試験データを用いて、原子力機構が開発してきた4K強度予測手法の実機TFコイル構造物用材料に対する予測精度について評価を実施したので報告する。

Wall-conditioning plasmas by ECRF heating in KSTAR

伊丹 潔; Hong, S.-H.*; Bae, Y.-S.*; 松川 誠; Kim, W.-C.*; KSTAR Team*

Journal of Nuclear Materials, 438, p.S930 - S935, 2013/07

https://doi.org/10.1016/j.jnucmat.2013.01.202

The plasma experiments to investigate the production of the helium ECWC plasmas and wall cleaning effects were carried out in the campaigns in 2010 and 2011 of KSTAR. Pulses of ECRF heating with fECRF = 110 GHz were injected into the vacuum vessel and the production of the ECWC plasma was measured by the plasma diagnostics. In 2010, the second harmonic of ECRF heating was applied at the position of = 1.97 . It was found that the ECRF injection vertical to the toroidal field, was essentially important to produce high density plasmas and the uniformity of the plasma is significantly changed by field pattern of and . In 2011, the fundamental ECRF heating was applied at the position of = 3.94 . It was demonstrated that a reference tokamak discharge successfully started up the plasma current after the wall conditioning by ECRF.