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171.
Motivated by mirror symmetry, we study certain integral representations of solutions to the Gel´fand-Kapranov-Zelevinsky (GKZ) hypergeometric system. Some of these solutions arise as period integrals for Calabi-Yau manifolds in mirror symmetry. We prove that for a suitable compactification of the parameter space, there exist certain special boundary points, which we called maximal degeneracy points, at which all solutions but one become singular.
172.
The solarization mechanism in a glass containing both Ce3+ and As5+, 16Na2O·11CaO·73SiO2:0.15AsOx·0.015CeOx (in mol.%), is newly proposed by elucidating the valence and coordination structure of arsenic after the photochemical reaction, the mechanism being traditionally expressed as ESR hyperfine quartets due to an As4+ ranging from 0.1 to 0.5 T built up on UV-irradiation and their line shape varied with the duration of the irradiation. The line shape analysis of the ESR spectra employing a computer simulation technique has led to the following conclusions; (1) As5+ is reduced to As4+ in the solarization process. (2) The geometry around the As4+ in the solarized glass is tetrahedral during the early stage and trigonal-pyramidal during the latter stage of the reaction. 相似文献
173.
A novel, cis‐transoidal poly‐(phenylacetylene) bearing a carboxybiphenyl group as the pendant (poly‐ 1 ) was prepared by polymerization of (4′‐ethoxycarbonyl‐4‐biphenylyl)acetylene with a rhodium catalyst followed by hydrolysis of the ester groups. Upon complexation with various chiral amines and amino alcohols in dimethyl sulfoxide (DMSO), the polymer exhibited characteristic induced circular dichroism (ICD) in the UV/Vis region due to the predominantly one‐handed helix formation of the polymer backbone as well as an excess of a single‐handed, axially twisted conformation of the pendant biphenyl group. Poly‐ 1 complexed with (R)‐2‐amino‐1‐propanol showed unique time‐dependent inversion of the macromolecular helicity. Furthermore, the preferred‐handed helical conformation of poly‐ 1 induced by a chiral amine was further “memorized” after the chiral amine was replaced with achiral 2‐aminoethanol or n‐butylamine in DMSO. In sharp contrast to the previously reported memory in poly((4‐carboxyphenyl)acetylene), the present helicity memory of poly‐ 1 was accompanied by memory of the twisted biphenyl chirality in the pendants. Unprecedentedly, the helicity memory of poly‐ 1 with achiral 2‐aminoethanol was found to occur simultaneously with inversion of the axial chirality of the biphenyl groups followed by memory of the inverted biphenyl chirality, thus showing a significant change in the CD spectral pattern. 相似文献
174.
Shirakawa E Ikeda D Yamaguchi S Hayashi T 《Chemical communications (Cambridge, England)》2008,(10):1214-1216
Alkyl Grignard reagents were found to be isomerized to more stable ones in high isomerization ratios (>99%) under cooperative catalysis by iron and copper, which promote isomerization of alkyl groups and transmetalation between Fe-Mg, respectively. 相似文献
175.
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177.
The Stevens rearrangement of N-allylic alpha-aryl amino acid-derived ammonium salts and the Sommelet-Hauser rearrangement of N-benzylic alpha-alkyl amino acid-derived ammonium salts are shown to proceed with remarkably high levels of diastereoselectivity. The methods presented in this work provide new routes to optically active alpha-quaternary alpha-aryl amino acid derivatives. 相似文献
178.
Analysis of Cu segregation to oxide–metal interface of Ni‐based alloy in a metal‐dusting environment
Takashi Doi Kazuyuki Kitamura Yoshitaka Nishiyama Nobuo Otsuka Takeo Kudo Masugu Sato Eiji Ikenaga Shigenori Ueda Keisuke Kobayashi 《Surface and interface analysis : SIA》2008,40(10):1374-1381
Hard X‐ray photoelectron spectroscopy (HX‐PES) has been realized using high‐brilliance synchrotron radiation. High‐energy photon excitation enables us to probe photoelectrons with larger escape depth compared to conventional PES. This allows us to conduct, without destruction, a study of the embedded interface of materials as the oxide‐ metal interface. We apply HX‐PES to investigate for Cu segregation in the oxide–metal interface during metal‐dusting corrosion. The effective concentration of Cu in the segregation was estimated a few times higher than the bulk concentration. These results on the interface layer can explain the variation in the corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
179.
Dr. Jiawei Zhang Dr. Daisuke Ishikawa Dr. Michael M. Koza Prof. Dr. Eiji Nishibori Dr. Lirong Song Dr. Alfred Q. R. Baron Prof. Dr. Bo B. Iversen 《Angewandte Chemie (International ed. in English)》2023,62(13):e202218458
Loosely bonded (“rattling”) atoms with s2 lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X-ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low-lying transverse phonons dominated by large In1+ z-axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In1+ 5s2 lone pair electrons and Te 5p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion. 相似文献
180.
Dr. Tomoyuki Ikai Sayaka Miyoshi Dr. Kosuke Oki Dr. Ranajit Saha Dr. Yuh Hijikata Prof. Eiji Yashima 《Angewandte Chemie (International ed. in English)》2023,62(20):e202301962
Fully π-conjugated ladder polymers with a spiral geometry represent a new class of helical polymers with great potential for organic nanodevices, but there is no precedent for an optically active helical ladder polymer totally composed of achiral units. We now report the defect-free synthesis and resolution of a fully π-conjugated helical ladder polymer with a rigid helical cavity, which has been achieved by quantitative and chemoselective acid-promoted alkyne benzannulations of a rationally designed, random-coil achiral polymer followed by chromatographic enantioseparation. Because of a sufficiently high helix-inversion barrier, the isolated excess one-handed helical ladder polymer with a degree of polymerization of more than 15 showed a strong circular dichroism with a dissymmetry factor of up to 1.7×10−2 and is thermally stable, maintaining its optical activity in solution even at 100 °C, as well-supported by molecular dynamics simulation. 相似文献