FCC構造を有する高・中工ントロピー合金の材料組織と力学特性：原子スケールの不均一性の観点から

京都大学新制・課程博士博士(工学)甲第23157号工博第4801号新制||工||1751(附属図書館)京都大学大学院工学研究科材料工学専攻(主査)教授 辻 伸泰, 教授 乾 晴行, 教授 安田 秀幸学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Universality of an impurity in a Bose-Einstein condensate

Universality is a powerful concept in physics, allowing one to construct physical descriptions of systems that are independent of the precise microscopic details or energy scales. A prime example is the Fermi gas with unitarity limited interactions, whose universal properties are relevant to systems ranging from atomic gases at microkelvin temperatures to the inner crust of neutron stars. Here we address the question of whether unitary Bose systems can possess a similar universality. We consider the simplest strongly interacting Bose system, where we have an impurity particle ("polaron") resonantly interacting with a Bose-Einstein condensate (BEC). Focusing on the ground state of the equal-mass system, we use a variational wave function for the polaron that includes up to three Bogoliubov excitations of the BEC, thus allowing us to capture both Efimov trimers and associated tetramers. Unlike the Fermi case, we find that the length scale associated with Efimov trimers (i.e., the three-body parameter) can strongly affect the polaron's behaviour, even at boson densities where there are no well-defined Efimov states. However, by comparing our results with recent quantum Monte Carlo calculations, we argue that the polaron energy is a \emph{universal} function of the Efimov three-body parameter for sufficiently low boson densities. We further support this conclusion by showing that the energies of the deepest bound Efimov trimers and tetramers at unitarity are universally related to one another, regardless of the microscopic model. On the other hand, we find that the quasiparticle residue and effective mass sensitively depend on the coherence length $\xi$ of the BEC, with the residue tending to zero as $\xi$ diverges, in a manner akin to the orthogonality catastrophe.Comment: 11 pages and 7 figures + supplemental materia

Direct observation of local chemical ordering in a few nanometer range in CoCrNi medium-entropy alloy by atom probe tomography and its impact on mechanical properties

ミディアムエントロピー合金の局所規則構造の原子レベル観察に成功 --新しい高強度合金の設計・開発に期待--. 京都大学プレスリリース. 2021-08-30.Local chemical ordering in CoCrNi medium-entropy alloy (MEA) was directly observed by the use of atom probe tomography. It was found that the densities of Cr, Co, and Ni were almost the same along the [111] direction, while those along the [001] direction were modulated to take a slightly enhanced and depleted value alternately within approximately 10 atomic layers corresponding to about 2 nm. The degree of modulation of Co and Ni was stronger than that of Cr. It was suggested that Cr-rich {001} atomic layers and (Ni + Co)-rich {001} layers tended to align mutually in the face-centered-cubic CoCrNi solid solution alloy. The mechanical properties of the MEA was found not to be affected by the presence of the local chemical ordering

オリーブに含まれるオリーブアナアキゾウムシ摂食刺激物質β-sitostery-D-glucoside

The olive weevil [Dyscerus perforatus (ROELOFS); Coleopetera; Curculionidae] is a native species in Japan and now the most serious pest of the olive trees. Originally, this weevil seemed to colonise Ligustrum japonicum Thumb. and L. obtusifolium Sieb. et Zucc, both of which belong to the same oleacea family as olive. However, when olive trees were introduced to Japan in 1908, the weevils immediately attacked the plants and soon preferred them to the former hosts. Unlike in the former hosts, where the weevils live in a low population density, it is extraordinary high in the case of olive trees and the subsequent assault becomes seriously damaging for the host plant. During the course of our study on the relationship between olive trees and olive weevils, we came to be interested in the possible chemical constituents that are responsible for host selection and attraction of the olive weevil to this plant. Previously, we reported that a secoiridoid gluconside, oleuropein, and some lignans, (-)-olivil and (+)-l-acetoxypinoresinol, from the olive tree stimulated the feeding habit of the weevil. In this study, we found a steroidal glucoside as another feeding stimulant component in the olive tree. Here, we describe the isolation, characterization and activity of this feeding stimulant.オリーブアナアキゾウムシは，モクセイ科のオリーブに多数寄生し甚大な被害を与えるため，オリーブ栽培上の深刻な問題となっている．我々は，これまでオリーブのメタノール抽出物から，オリーブアナアキゾウムシの摂食刺激成分として，雌雄に活性を示すセコイリドイド配糖体1種と，雌に特異的に活性を持つ2種のリグナン類を得た．さらに今回，同じメタノール抽出物から，活性物質としてステロイド配糖体であるβ-sitosteryl-D-glucosideを得た．この成分は雌雄に対してほぼ同等の摂食刺激活性を示した

分子系統学における代数的方法

要旨あり多様性と進化の統計解析研究詳