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青柳 登; 元川 竜平; 奥村 雅彦; 上田 祐生; 斉藤 拓巳*; 西辻 祥太郎*; 田口 富嗣*; 蓬田 匠; 佐崎 元*; 池田 篤史
Communications Chemistry (Internet), 7, p.128_1 - 128_13, 2024/06
被引用回数：0 パーセンタイル：0.00(Chemistry, Multidisciplinary)Dissipative structures often appear as an unstable counterpart of ordered structures owing to fluctuations that do not form a homogeneous phase. Even a multiphase mixture may simultaneously undergo one chemical reaction near equilibrium and another one that is far from equilibrium. Here, we observed in real-time crystal seed formation and simultaneous nanocrystal aggregation proceeding from tetravalent cerium complexes to ceria nanoparticles in an acidic aqueous solution and investigated the resultant hierarchical nanoarchitecture. The formed particles exhibited two very different size ranges. The hierarchically assembled structures in solutions were ceria colloids, viz. primary core clusters of crystalline ceria and secondary clusters assembled through surface ions. Such self-assembly is widespread in multi-component complex fluids, paradoxically moderating hierarchical reactions. Stability and instability are not only critical but also complementary for co-optimization around the nearby free energy landscape prior to bifurcation.
斉藤 拓巳*; 元川 竜平; 大窪 貴洋*; 三浦 大輔*; 熊田 高之
Environmental Science & Technology, 57(26), p.9802 - 9810, 2023/07
被引用回数：1 パーセンタイル：13.27(Engineering, Environmental)Aggregation of humic acids (HAs) were studied by small-angle neutron and X-ray scattering techniques. The combination of these techniques enables us to examine aggregation structures of heterogeneous HA particles. Two HAs with distinctive compositions were examined; a commercial HA (PAHA) and a HA extracted from deep sedimentary groundwater (HHA). While macroscopic coagulation tests showed that these HAs were stable in solutions except for HHA at pH 
6, small-angle neutron scattering (SANS) and X-ray scattering (SAXS) revealed that they formed aggregates with the sizes exceeding sub-micrometer length scale. The SAXS curves of PAHA remarkably varied with pD, whereas the SANS curves did not. With the help of theoretical fittings, it was revealed that PAHA aggregates consisted of two domains: poorly hydrated cores and well-hydrated proton-rich shells. The cores are (dis)aggregated with pD inside the aggregates of the shell. The SANS and SAXS curves of HHA resemble each other, and their intensities at low q increased with a decrease of pD, indicating the formation of homogeneous aggregates. This study revealed that distinctive aggregation behaviors exist in humic substances with heterogeneous structures like PAHA, which is invaluable for their roles in the fate of contaminants or nutrients in aqueous environments.
小松 遊矢*; 清水 亮太*; 佐藤 龍平*; Wilde, M.*; 西尾 和記*; 片瀬 貴義*; 松村 大樹; 齋藤 寛之*; 宮内 雅浩*; Adelman, J. R.*; et al.
Chemistry of Materials, 34(8), p.3616 - 3623, 2022/04
被引用回数：17 パーセンタイル：76.21(Chemistry, Physical)Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YO
H
) epitaxial thin films. The temperature (
) dependence of the electrical resistivity (
) of the films transforms from insulating to metallic (
) under ultraviolet laser illumination. The sample is heated (125 
C) under an Ar atmosphere to recover its original insulating state. The films recover their original metallic conductivity when subsequently subjected to ultraviolet laser illumination, showing repeatable photoinduced insulator-to-metal transition. First principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.
小林 大志*; 中嶋 翔梧*; 元川 竜平; 松村 大樹; 斉藤 拓巳*; 佐々木 隆之*
Langmuir, 35(24), p.7995 - 8006, 2019/06
被引用回数：5 パーセンタイル：18.85(Chemistry, Multidisciplinary)We report the hierarchical structure of zirconium hydroxide after aging at different temperatures to elucidate the factors governing zirconium solubility in aqueous solutions. Zirconium hydroxide solid phases after aging at 25, 40, 60, and 90C under acidic to alkaline conditions were investigated using extended X-ray absorption fine structure (EXAFS) and wide- and small-angle X-ray scattering (WAXS and SAXS) techniques to reveal the bulk and surface structures of the solid phases from the nanoscale to submicroscale. After aging at 25 C, the fundamental building unit of the solid phase was a zirconium hydroxide tetramer. The tetramers formed primary particles approximately 3 nm in size, which in turn formed aggregates hundreds of nanometers in size. This hierarchical structure was found to be stable up to 60 C under acidic and neutral conditions and up to 40 C under alkaline conditions. After aging at 90 C under acidic conditions and at 60 and 90 C under alkaline conditions, the WAXS and EXAFS measurements suggested the crystallization of the solid phase. The transformation of the solid-phase structure by temperature was discussed in relation to the solubility product to understand the solubility-limiting solid phase. The solubility of zirconium hydroxide after aging at different temperatures was governed not only by the size of the primary particles, but also by their surface configuration.
宮澤 忠士*; 浅利 勇紀*; 三好 和義*; 梅野 太輔*; 斎藤 恭一*; 永谷 剛*; 吉川 直人*; 元川 竜平; 小泉 智*
日本海水学会誌, 64(6), p.360 - 365, 2010/12
Cation-exchange membranes containing a sulfonic acid group were prepared by electron-beam-induced graft polymerization of sodiumstyrene sulfonate (SSS) onto a nylon-6 film with a thickness of 25 
m. The lamella sizes and lamella-to-lamella intervals of theresultant cation-exchange membranes (SSS membranes) were evaluated by X-ray diffraction (XRD) analysis and small-angle neutron scattering (SANS), respectively. With increasing degrees of grafting, the lamella size decreased, whereas the lamella-to-lamella intervalincreased. This can be explained by that the poly-SSS chain grafted to the periphery of the lamella of nylon 6 partially destroys the lamellaand invades the amorphous domain among the lamella. The SSS membrane with a degree of grafting of 150% exhibited a similarperformance in the electrodialysis of 0.5 M sodium chloride as a current cation-exchange membrane and possessed the lamella sizesand lamella-to-lamella intervals of 7.6 and 13 nm, respectively.
宮村 浩子; 品野 勇治*; 宮代 隆平*; 斎藤 隆文*
情報処理学会論文誌; 数理モデル化と応用(インターネット), 2(2), p.103 - 112, 2009/03
分枝限定法を用いて整数計画問題を解く際に、どのような分枝戦略を選択するかは重要な問題である。分枝戦略の良し悪しは、生成される子問題の数,分枝限定木の深さ,総計算時間などに大きな影響を与える。しかしながら、大規模な数理計画問題では、分枝限定木の生成過程における出力は大量のログデータとなってしまい、それぞれの分枝戦略がどのように影響を与えているのか直感的な把握が難しい。そこで本研究では、分枝限定木の生長過程を可視化するシステムを提案する。本システムにより、分枝戦略の違いが子問題の生成過程に及ぼす影響を視覚的に捉えることができる。
西山 哲*; 上原 真一*; 矢野 隆夫*; 斉藤 竜平*; 内田 雅大; 澤田 淳; 武部 篤治
JNC TY8400 2005-007, 70 Pages, 2005/03
JNC-TY8400-2005-007.pdf:2.24MB
本研究では,岩盤不連続面のせん断時における透水特性を把握するために,せん断透水同時試験装置の開発を行い,人工供試体を用いてせん断透水試験を行った。せん断時の垂直方向の拘束形式としては垂直応力一定試験と垂直剛性一定試験を採用しており,基本的なパラメータである垂直応力,垂直剛性Kv,不連続面表面形状および動水勾配Iなどが透水特性に与える影響について考察した。また,開発したLGA解析コードを用いて,開口幅をパラメータとした平行平板中の流体解析を実施した。そして,その流体解析結果から,開口幅,動水勾配と流量の関係について検討を行い,LGA法の適用性を確認した。
青柳 登; 元川 竜平; 斉藤 拓巳*; 奥村 雅彦; 池田 篤史
no journal, ,
We aimed at finding out a structural order and interaction between intra/inter clustering molecules composed of tetravalent cerium ions and others at high concentration: e.g. ranging from 50.0 mM to 1.0 M. Surprisingly, we confirmed that the "giant cluster" with a diameter of ca. 25.4 nm was formed after examining X-ray small-angle scattering patterns in detail. Plus, this diameter enlarges as time evolves. Moreover, we demonstrate detailed analysis as well as model construction for theoretical calculation and verification on the formation and characteristics, whether or not agglomeration of primary clusters, of giant clusters.
