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排序方式: 共有214条查询结果,搜索用时 11 毫秒
101.
H Nonami F Wu R P Thummel Y Fukuyama H Yamaoka R Erra-Balsells 《Rapid communications in mass spectrometry : RCM》2001,15(23):2354-2373
In an effort to gain an understanding of the processes governing ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI), direct comparison was made of the mass spectra of proteins, carbohydrates and synthetic polymers (polyethylene glycol, polyester and polyamide) by using pyridylindoles, pyridoindoles and pyridylpyridoindoles as UV (337 nm)-MALDI-TOFMS matrices in positive and negative ion mode. In order to study the combined effect of the indole N-H and the pyridine nitrogen of the MALDI matrix on the desorption/ionization process in MALDI, compounds were selected that include either or both of these functions in their structure. Within the compounds studied only those that possess simultaneously both functions in a 1,4-relation behave as very good matrices for proteins. These compounds also work as matrices for some carbohydrates and synthetic polymers used as analytes in the present study. Some of the compounds were also found to be useful for the post-source decay (PSD) analysis of cyclodextrins in positive and negative ion mode. In several cases we also examined the matrix behavior of the corresponding N-methylindole derivatives. 相似文献
102.
Tomohiro Hirano Ryosuke Yamaoka Takamasa Miyazaki Koichi Ute 《Journal of polymer science. Part A, Polymer chemistry》2010,48(24):5718-5726
Radical polymerization of N‐tert‐butoxycarbonylacrylamide (NBocAAm) in toluene at low temperatures in the presence of the fluorinated alcohols, 2,2,2‐trifluoroethanol, 1,1,1,3,3,3‐hexafluoro‐2‐propanol, and nonafluoro‐tert‐butanol, afforded atactic, heterotactic, and syndiotactic polymers, respectively. NMR analysis revealed that the fluorinated alcohols formed hydrogen bonding‐assisted complexes with NBocAAm, with different structures. The difference in the structures of the complexes was responsible for the differences in the induced stereospecificities. Based on the structures of the complexes between NBocAAm and the fluorinated alcohols, mechanisms for the three kinds of stereospecific radical polymerizations are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
103.
Akihiro Sakoda Yuu Ishimori Katsumi Hanamoto Takahiro Kataoka Atsushi Kawabe Kiyonori Yamaoka 《Radiation measurements》2010,45(2):204-210
Some models have already been developed to explain the effect of moisture content on the radon emanation fraction of soil. For this purpose, “microscopic” soil models, which are easy to deal with mathematically but cannot take grain size into consideration, have been designed. These previous models consist basically of two opposite grain surfaces and pores between the grains. In the present study, in order to study the effect of not only moisture content but also grain size, we present a simple modeling approach based on two “macroscopic” soil models: (1) a single-grain model and (2) a multiple-grain model. The latter model represents a configuration of spherical grains packed in a simple cubic structure. Based on these soil models and general assumptions, the radon emanation fraction was calculated as a function of grain size or moisture content by Monte Carlo simulation. The results for the multiple-grain model show that the radon emanation fraction is markedly increased with grain sizes ranging from 10 to 100 μm and reaches a constant value of 50% when moisture content is 0% and the radium is uniformly distributed on the grain surface. Moreover, a drastic increase is seen at smaller grain sizes with increasing moisture content. From these results, we concluded that the calculation of radon emanation depends greatly on the pore size between a Ra-bearing grain and a neighboring grain. The validity of the model was also evaluated by comparison to experimental data. 相似文献
104.
Organocatalytic Activation of the Leaving Group in the Intramolecular Asymmetric SN2′ Reaction 下载免费PDF全文
Yusuke Kuroda Dr. Shingo Harada Akinori Oonishi Dr. Yousuke Yamaoka Prof. Dr. Ken‐ichi Yamada Prof. Dr. Kiyosei Takasu 《Angewandte Chemie (International ed. in English)》2015,54(28):8263-8266
A Brønsted‐acid‐catalyzed intramolecular enantioselective SN2′ reaction was developed utilizing trichloroacetimidate as a leaving group. The findings indicated that dual activation of the substrates is operative. This metal‐free allylic alkylation allows highly enantioselective access to 2‐vinylpyrrolidines bearing various substituents. 相似文献
105.
Kozo Matsumoto Hironobu Shimazu Masaki Deguchi Hitoshi Yamaoka 《Journal of polymer science. Part A, Polymer chemistry》1997,35(15):3207-3216
Anionic polymerizations of 1,1-dimethylsilacyclobutane, 1,1-diethylsilacyclobutane and 1-methyl-1-phenylsilacyclobutane were investigated. Addition of 5 mol % of butyllithium to a solution of 1,1-dimethylsilacyclobutane in THF-hexane (1 : 1) at −48°C provided poly(1,1-dimethylsilabutane) in 99% yield. Mn and Mw/Mn of the obtained polymer were 2400 and 1.10. This polymerization proceeded with a living nature. Mn increased in proportion as the yield of polymer increased. Addition of the second fresh feed of the monomer to the reaction mixture restarted polymerization of the second monomer at the same rate as in the initial stage. Addition of styrene to the living poly(1,1-dimethylsilabutane) provided a poly(1,1-dimethylsilabutane-b-styrene) block copolymer. It was also found that a polymerization of 1,1-diethylsilacyclobutane in THF-hexane at −48°C showed a living nature. In contrast, a polymerization of 1-methyl-1-phenylsilacyclobutane in THF at −78°C did not show a living nature. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3207–3216, 1997 相似文献
106.
Takanori Takahashi Kazuhiro Ikegaya Hirohmi Watanabe Nobukazu Miyagawa Shigeru Takahara Tsuguo Yamaoka 《先进技术聚合物》2000,11(6):307-315
A novel water‐dispersible reactive microgel, which had a diameter of 40–90 nm, was synthesized for photopolymer materials. The microgels have segments with substituted ammonium groups, to provide water solubility, in their polymer networked structure. It has unsaturated groups connected to the quaternary nitrogens by ionic bonding (I‐type microgel). The I‐type microgel was compared with one that has methacryloyl groups connected with the quaternary nitrogens of the microgel by covalent bonding (C‐type microgel). The I‐type microgels were able to separately control the modified amount of quaternary nitrogen and methacryloyl group. In the presence of 2,4‐diethylthioxantone as a photoinitiator and pentaerthritol triacrylate as a crosslinker, the photopolymer containing the C‐type or I‐type microgels had sensitivity high enough for practical use. Not only the amount of the methacryloyl group of the microgel but the amount of the quaternary nitrogen affected the sensitivity and the rate of polymerization of the water‐dispersible photopolymer containing the I‐type microgels. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
107.
This paper deals with the global existence and nonexistence of solutions of the second-order nonlinear differential equation (φ(x′))′+λφ(x)=0 satisfying x(0)=x0 and x′(0)=x1, where λ is a positive parameter and φ:(−ρ,ρ)→(−σ,σ) with 0<ρ?∞ and 0<σ?∞ is strictly increasing odd bijective and continuous on (−ρ,ρ). Necessary and sufficient conditions are obtained for the initial value problem to have a unique global solution which is oscillatory and periodic. Examples are given to illustrate our main result. Finally, a nonexistence result for the equation with a damping term is discussed as an application to our result. 相似文献
108.
Luca M. Cavinato Keiko Yamaoka Sophia Lipinski Vladimir Calvi Dominique Wehenkel Richard van Rijn Ken Albrecht Rubén D. Costa 《Advanced functional materials》2023,33(35):2302483
A rational implementation and optimization of thermally activated delayed fluorescent (TADF) dendrimer emitters in light-emitting electrochemical cells (LECs) sets in the Dendri-LEC family. They feature outstanding stabilities (90/1050 h for green/yellow devices) that are comparable to the best green/yellow Ir(III)-complexes (450/500 h) and conjugated polymers (33/5500 h), while offering benefits of low-cost synthesis and easy upscaling. In particular, a fundamental molecular design that capitalizes on exchanging peripheral substituents (tert-butyl vs methoxy) to tune photophysical, electrochemical, morphological, and ion conductivity features in thin films is rationalized by temperature-dependent steady-state and time-resolved emission spectroscopy, cyclic voltammetry, atomic force microscopy, and electrochemical impedance spectroscopy techniques. Herein, a TADF mechanism associated to a reduced photoluminescence quantum yield, but an enhanced electrochemical stability and ion conductivity enables to clarify the reduced device efficiency and brightness (4.0 lm W−1@110 cd m−2 vs 3.2 lm W−1@55 cd m−2) and increased stability (90 vs 1050 h) upon using methoxy groups. What is more, this substitution enables an excellent compatibility with biogenic electrolytes keeping device performances (1.9 lm W−1@35 cd m−2 and 1300 h), while graphene-devices achieve on par figures to traditional indium–tin oxide-devices. Overall, this work establishes the bright future of dendrimer emitters toward highly stable and truly sustainable lighting sources. 相似文献
109.
Jitsuro Sugie Kazuhisa Kita Naoto Yamaoka 《Annali di Matematica Pura ed Applicata》2002,181(3):309-337
Our concern is to solve the oscillation problem for the non-linear self-adjoint differential equation (a(t)x’)’+b(t)g(x)=0, where g(x) satisfies the signum condition xg(x)>0 if x≠0, but is not assumed to be monotone. Sufficient conditions and necessary conditions are given for all non-trivial solutions
to be oscillatory. The obtained results show that the number 1/4 is a critical value for this problem. This paper takes a
different approach from most of the previous research. Proof is given by means of phase plane analysis of systems of Liénard
type. Examples are included to illustrate the relation between our theorems and results which were given by Cecchi, Marini
and Villari.
Received: January 5, 2001?Published online: June 11, 2002 相似文献
110.
Naoto Yamaoka 《Journal of Mathematical Analysis and Applications》2007,325(2):932-948
This paper is concerned with the oscillation problem for the nonlinear differential equation with a damping term,