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排序方式: 共有328条查询结果,搜索用时 15 毫秒
1.
Topological “interfacial” polymer chemistry: Dependency of polymer “shape” on surface morphology and stability of layer structures when heating organized molecular films of cyclic and linear block copolymers of n‐butyl acrylate‐ethylene oxide 下载免费PDF全文
Qi Meng Satoshi Honda Yasuyuki Tezuka Takuya Yamamoto Atsuhiro Fujimori 《Journal of Polymer Science.Polymer Physics》2016,54(4):486-498
The “topological polymer chemistry” of amphiphilic linear and cyclic block copolymers at an air/water interface was investigated. A cyclic copolymer and two linear copolymers (AB‐type diblock and ABA‐type triblock copolymers) synthesized from the same monomers were used in this study. Relatively stable monolayers of these three copolymers were observed to form at an air/water interface. Similar condensed‐phase temperature‐dependent behaviors were observed in surface pressure–area isotherms for these three monolayers. Molecular orientations at the air/water interface for the two linear block copolymers were similar to that of the cyclic block copolymer. Atomic force microscopic observations of transferred films for the three polymer types revealed the formation of monolayers with very similar morphologies at the mesoscopic scale at room temperature and constant compression speed. ABA‐type triblock linear copolymers adopted a fiber‐like surface morphology via two‐dimensional crystallization at low compression speeds. In contrast, the cyclic block copolymer formed a shapeless domain. Temperature‐controlled out‐of‐plane X‐ray diffraction (XRD) analysis of Langmuir–Blodgett (LB) films fabricated from both amphiphilic linear and cyclic block copolymers was performed to estimate the layer regularity at higher temperatures. Excellent heat‐resistant properties of organized molecular films created from the cyclic copolymer were confirmed. Both copolymer types showed clear diffraction peaks at room temperature, indicating the formation of highly ordered layer structures. However, the layer structures of the linear copolymers gradually disordered when heated. Conversely, the regularity of cyclic copolymer LB multilayers did not change with heating up to 50 °C. Higher‐order reflections (d002, d003) in the XRD patterns were also unchanged, indicative of a highly ordered structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 486–498 相似文献
2.
Tailoring D‐Amino Acid Oxidase from the Pig Kidney to R‐Stereoselective Amine Oxidase and its Use in the Deracemization of α‐Methylbenzylamine 下载免费PDF全文
Kazuyuki Yasukawa Dr. Shogo Nakano Prof. Dr. Yasuhisa Asano 《Angewandte Chemie (International ed. in English)》2014,53(17):4428-4431
The deracemization of racemic amines to yield enantioenriched amines using S‐stereoselective amine oxidases (AOx) has recently been attracting attention. However, R‐stereoselective AOx that are suitable for deracemization have not yet been identified. An R‐stereoselective AOx was now evolved from porcine kidney D ‐amino acid oxidase (pkDAO) and subsequently use for the deracemization of racemic amines. The engineered pkDAO, which was obtained by directed evolution, displayed a markedly changed substrate specificity towards R amines. The mutant enzyme exhibited a high preference towards the substrate α‐methylbenzylamine and was used to synthesize the S amine through deracemization. The findings of this study indicate that further investigations on the structure–activity relationship of AOx are warranted and also provide a new method for biotransformations in organic synthesis. 相似文献
3.
This paper considers a Lotka–Volterra predator–prey model with predators receiving an environmental time-variation. For such a system, a unique interior equilibrium is shown to be globally asymptotically stable if the time-variation is bounded and weakly integrally positive. Our result tells that the equilibrium can be stabilized even by nonnegative functions that make the limiting system structurally unstable. Numerical simulations are also shown to illustrate the result and to suggest that cases with time-variation acting on predators have larger-scale convergence to the equilibrium than population dynamics with time-variation acting on prey. 相似文献
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Zircon-type compounds LnCrO4 (Ln=Nd, Sm, and Dy) were prepared. Their precise crystal structures at room temperature were determined from X-ray diffraction measurements. These compounds have a tetragonal system with space group I41/amd. Magnetic susceptibility and specific heat measurements have been performed for all the compounds in the temperature range between 1.8 and 300 K. For NdCrO4, an antiferromagnetic transition was found at 25.2 K. SmCrO4 and DyCrO4 show magnetic transitions at 15.0 and 22.8 K, respectively. In addition, structural phase transitions were observed at 58.5 and 31.2 K, respectively. For DyCrO4, the crystal structure below the transition temperature was determined by low-temperature powder X-ray diffraction measurements to be orthorhombic with space group Imma. 相似文献
7.
Kotaro Nagatani Yunosuke Hoshino Haruka Tezuka Masahisa Nakada 《Tetrahedron letters》2017,58(10):959-962
A synthetic pathway to the C-ring fragment of cotylenin A which emerged from our retrosynthetic analysis of cotylenin A is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of the α-diazo-β-keto ester bearing 2,4,6-trimethylphenyl group as the ester part has been found to afford the crystalline product with high ee, which allowed to establish the approach to the C-ring fragment which required ten-pot operations. The developed approach would be beneficial to a large scale synthesis of the C-ring fragment for the total synthesis of cotylenin A. 相似文献
8.
Keisuke Akita Youhi Morii Hisashi Nakamura Takuya Tezuka Kaoru Maruta 《Proceedings of the Combustion Institute》2021,38(2):2247-2255
Two-dimensional axisymmetric numerical simulation reproduced flames with repetitive extinction and ignition (FREI) in a micro flow reactor with a controlled temperature profile with a stoichiometric n-heptane/air mixture, which have been observed in the experiment. The ignition of hot flame occurred from consumption reactions of CO that was remained in the previous cycle of FREI. Between extinction and ignition locations of hot flames, several other heat release rate peaks related to cool and blue flames were observed for the first time. After the extinction of the hot flame, cool flame by the low-temperature oxidation of n-heptane appeared first and was stabilized in a low wall temperature region. In the downstream of the stable cool flame, a blue flame by the consumption reactions of cool flame products of CH2O and H2O2 appeared. After that, the hot flame ignition occurred from the remaining CO in the downstream of the blue flame. Then after the next hot flame ignition, the blue flame was swept away by the propagating hot flame. Soon before the hot flame merged with the stable cool flame, the hot flame propagation was intensified by the cool flame. After the hot flame merged with the stable cool flame, the hot flame reacted with the incoming fresh mixture of n-C7H16 and O2. 相似文献
9.
Takuya Adachi Yasuhisa Yamamura Mafumi Hishida Mao Ueda Shunji Ito 《Liquid crystals》2013,40(11):1340-1344
Molecular dynamics in the soft crystal, E phase of 6-octyl-2-phenylazulene was studied by X-ray diffraction, and dielectric and Fourier transform infrared spectroscopies. Clear dielectric dispersion is observed due to the head-to-tail disordering in a kHz range around 400 K. The CH stretching frequencies exhibit more pronounced shifts at the phase transition point from the high-temperature ordered crystal to the E phase than that at the melting from the E phase to the isotropic liquid. The results are discussed in comparison with a typical E series, 4-n-alkyl-4′-isothiocyanatobiphenyl (n being the number of carbon atoms in the alkyl group). 相似文献
10.
The author reports here a thorough investigation of structural and magnetic properties of Co2FeAl0.5Si0.5 Heusler alloy films, and the tunnel magnetoresistance effect for junctions with Co2FeAl0.5Si0.5 electrodes, spin injection into GaAs semiconductor from Co2FeAl0.5Si0.5, and spin filtering phenomena for junctions with CoFe2O4 ferrite barrier. It was observed that tunnel magnetoresistance ratio up to 832%(386%) at 9 K (room temperature), which corresponds to the tunnel spin polarization of 0.90 (0.81) for the junctions using Co2FeAl0.5Si0.5 Heusler electrodes by optimizing the fabrication condition. It was also found that the tunnel magnetoresistance ratio are almost the same between the junctions with Co2FeAl0.5Si0.5 Heusler electrodes on Cr buffered (1 0 0) and (1 1 0) MgO substrates, which indicates that tunnel spin polarization of Co2FeAl0.5Si0.5 for these two direction are almost the same. The next part of this paper is a spin filtering effect using a Co ferrite. The spin filtering effect was observed through a thin Co-ferrite barrier. The inverse type tunnel magnetoresistance ratio of −124% measured at 10 K was obtained. The inverse type magnetoresistance suggests the negative spin polarization of Co-ferrite barrier. The magnetoresistance ratio of −124% corresponds to the spin polarization of −0.77 by the Co-ferrite barrier. The last part is devoted to the spin injection from Co2FeAl0.5Si0.5 into GaAs. The spin injection signal was clearly obtained by three terminal Hanle measurement. The spin relaxation time was estimated to be 380 ps measured at 5 K. 相似文献