トポタクティック反応による遷移金属酸化物薄膜のアニオン制御

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 長谷川 哲也, 東京大学教授 塩谷 光彦, 東京大学教授 西原 寛, 東京大学教授 鍵 裕之, 東京大学准教授 岡林 潤University of Tokyo(東京大学

Implementation and Evaluation of an Automated Question Generation Module for Question and Answer about the Content of an English Story

英語学習において，長文を読み，その内容に関する質問に解答する学習方法は一般的であり，実際の教育現場や学習支援システムで採用されている．しかし，これまでの学習支援システムではあらかじめ用意された質問を用いるため，学習者の理解状態に合致した質問を出題することは非常に困難である．本論文では，英語長文読解学習の際に学習者の理解状態に適した質問を行うために必要な質問文自動生成について述べる．質問の生成は，１文についての質問生成，同義語・反義語を用いた質問生成，修飾語句を用いた質問生成，文の合成を用いた質問生成，時空関係を用いた質問生成という５種類のモジュールを利用して行われる．評価として中学生レベルの問題集を人手で調査したところ，本論文で提案した質問文の生成法で約80％の質問が生成可能であることがわかった．また，実際に中学校２年生と３年生の英語の教科書の物語の英文301文について質問文自動生成を行った結果，生成した質問文1977文中1848文（約93%）が意味的に適格な文であった．本研究の一部は，文部省科学研究費補助金奨励研究(A) (No．10780113)の援助による

Time-resolved serial femtosecond crystallography reveals early structural changes in channelrhodopsin

X線自由電子レーザーを用いて、光照射によるチャネルロドプシンの構造変化の過程を捉えることに成功. 京都大学プレスリリース. 2021-03-26.Channelrhodopsins (ChRs) are microbial light-gated ion channels utilized in optogenetics to control neural activity with light . Light absorption causes retinal chromophore isomerization and subsequent protein conformational changes visualized as optically distinguished intermediates, coupled with channel opening and closing. However, the detailed molecular events underlying channel gating remain unknown. We performed time-resolved serial femtosecond crystallographic analyses of ChR by using an X-ray free electron laser, which revealed conformational changes following photoactivation. The isomerized retinal adopts a twisted conformation and shifts toward the putative internal proton donor residues, consequently inducing an outward shift of TM3, as well as a local deformation in TM7. These early conformational changes in the pore-forming helices should be the triggers that lead to opening of the ion conducting pore

Real-time observation of X-ray-induced intramolecular and interatomic electronic decay in CH2I2

The increasing availability of X-ray free-electron lasers (XFELs) has catalyzed the development of single-object structural determination and of structural dynamics tracking in realtime. Disentangling the molecular-level reactions triggered by the interaction with an XFEL pulse is a fundamental step towards developing such applications. Here we report real-time observations of XFEL-induced electronic decay via short-lived transient electronic states in the diiodomethane molecule, using a femtosecond near-infrared probe laser. We determine the lifetimes of the transient states populated during the XFEL-induced Auger cascades and find that multiply charged iodine ions are issued from short-lived (similar to 20 fs) transient states, whereas the singly charged ones originate from significantly longer-lived states (similar to 100 fs). We identify the mechanisms behind these different time scales: contrary to the short-lived transient states which relax by molecular Auger decay, the long-lived ones decay by an interatomic Coulombic decay between two iodine atoms, during the molecular fragmentation

Characterizing crystalline defects in single nanoparticles from angular correlations of single-shot diffracted X-rays

Characterizing and controlling the uniformity of nanoparticles is crucial for their application in science and technology because crystalline defects in the nanoparticles strongly affect their unique properties. Recently, ultra-short and ultra-bright X-ray pulses provided by X-ray free-electron lasers (XFELs) opened up the possibility of structure determination of nanometre-scale matter with angstrom spatial resolution. However, it is often difficult to reconstruct the 3D structural information from single-shot X-ray diffraction patterns owing to the random orientation of the particles. This report proposes an analysis approach for characterizing defects in nanoparticles using wide-angle X-ray scattering (WAXS) data from free-flying single nanoparticles. The analysis method is based on the concept of correlated X-ray scattering, in which correlations of scattered X-ray are used to recover detailed structural information. WAXS experiments of xenon nanoparticles, or clusters, were conducted at an XFEL facility in Japan by using the SPring-8 Angstrom compact free-electron laser (SACLA). Bragg spots in the recorded single-shot X-ray diffraction patterns showed clear angular correlations, which offered significant structural information on the nanoparticles. The experimental angular correlations were reproduced by numerical simulation in which kinematical theory of diffraction was combined with geometric calculations. We also explain the diffuse scattering intensity as being due to the stacking faults in the xenon clusters