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91.
Preparation and characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes 总被引:2,自引:0,他引:2
Tomitsugu Taguchi Naoki Igawa Hiroyuki Yamamoto Shin-ichi Shamoto Shiro Jitsukawa 《Physica E: Low-dimensional Systems and Nanostructures》2005,28(4):431-438
Preparation conditions of single-phase SiC nanotubes and C-SiC coaxial nanotubes were investigated. The characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes were carried out. The SiC nanowires, which were made of the catenated SiC grains of 50–200 nm in diameter, were obtained in carbon nanotubes reacted at 1450 °C. The only C-SiC coaxial nanotubes were formed at 1300 °C. A few single-phase SiC nantoubes were synthesized at 1200 °C for 100 h. More than half number of nanotubes reacted at 1200 °C for 100 h were altered to single-phase SiC nantoubes by heat treatment of 600 °C for 1 h in air since the remained carbon was removed. The energy dispersive X-ray spectroscopy analysis revealed that the atomic ratio of Si to C in single-phase SiC nanotubes was almost 1; these single-phase SiC nanotubes consisted of near-stoichiometric SiC grains. 相似文献
92.
93.
Kayoko Tahara Emi Makii Shiro Iijima Yoshihiro Abe Masataka Mochizuki 《Analytical sciences》2008,24(7):935-938
The electrochemical oxidation of (+/-)-alpha-tocopherol on a porous graphite electrode was performed in the presence of methanol, and successive separation and detection of the products were performed by an on-line liquid chromatography/mass spectrometry system. Three products were identified, one of which was determined to be alpha-tocopheryl quinone, because its m/z was 469 [M+Na](+). The other two products showed identical mass and UV spectra, and were suspected to be diastereomers of 9-methoxy-alpha-tocopheron, because their molecular weights were m/z 483 [M+Na](+), and also because it is known that the chemical oxidation of alpha-tocopherol by benzoyl peroxide or N-bromosuccinimide in the presence of methanol should provide 9-methoxy-alpha-tocopheron. To confirm that these two compounds were diastereomers, a circular dichroism detector was used. The signs of both peaks detected by the circular dichroism detector at 230 nm were opposite. In addition to observations of identical mass and ultraviolet spectra, these results indicated that the two products were diastereomers of 9-methoxy-alpha-tocopheron, whose stereochemistry is different at the newly generated chiral center of the 9-position. The on-line use of a circular dichroism detector with an electrochemical cell/liquid chromatography system may expand the utility of the system to study the metabolism of a chiral drug. 相似文献
94.
95.
Raman spectra of anthracene mono- and di-negative ions in tetrahydrofuran solution were obtained by HeNe and Ar+ laser exciting lines. In addition to some frequency shifts from neutral anthracene, remarkable enhancement of intensities by the resonance Raman effect was observed for many aromatic ring vibrations. 相似文献
96.
Yoshio Kato Shiro Kido Manabu Yamamoto Tsutomu Hashimoto 《Journal of Polymer Science.Polymer Physics》1974,12(7):1339-1345
To establish optimum operating conditions for high-speed gel-permeation chromatography (GPC), the effects of column packing particle size, solvent flow rate, and column length on the separation efficiency have been investigated by using monodisperse polystyrene samples and polystyrene gel columns (TSK-GEL column, Type-H). Decreasing the particle size of the column packing reduces the time required to obtain a given resolution. Monodisperse polystyrene standards were measured under the optimum operating conditions established (gel particle size 5 μ, column length 2 ft, flow rate 2.5 ml/min). The molecular weight distribution of a polymer mixture was determined in less than 10 min with the same accuracy as by the conventional GPC. Such short analysis time enables one to use GPC for in-plant quality control. 相似文献
97.
The resonance Raman effect of I2 was observed in chloroform, benzene-d6 and tetrahydrofuran solutions with eleven exciting frequencies by Ar+, Kr+ and He-Ne lasers. Excitation profiles obtained for the νI-I fundamental in benzene-d6 and tetrahydrofuran showed apparently different features from that of chloroform. It is demonstrated in a simulative calculation that the anomalous profile in the former two solvents could be caused by the interference between partial contributions to the scattering tensor, one from the locally excited state responsible for the visible absorption and the other from the charge-transfer state, both of the complex formed. 相似文献
98.
Novel chiral phosphonoacetates bearing a stereogenic phosphorus atom were successfully synthesized by enzyme-catalyzed kinetic resolution of racemic phosphonoacetates. 相似文献
99.
A self-consistent evaluation of particle-hole type matrix elements for density-dependent interactions is presented. Effects of rearrangement are evaluated. 相似文献
100.
We present an experimental study of the light emission from dye-doped polymer random media dispersed with TiO2 particles of various sizes, shapes, and structures. Random lasing with nonresonant feedback, similar to that for spherically
shaped particles that are used for conventional random lasers, is observed for almost all types of particles and aggregates.
The efficiency of random lasing for each medium is analyzed using the relationship between the emission spectrum and the transport
mean free path (TMFP), which is measured by enhanced backscattering experiments. Results show that the peak emission intensity
depends strongly on the particle shape and structure, whereas the spectral linewidth is governed by the TMFP. 相似文献