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991.
Woo Hyung Jeon Jeong‐Yu Son Sun‐Eung Kim Phil Ho Lee 《Advanced Synthesis \u0026amp; Catalysis》2015,357(4):811-817
An efficient phosphaannulation via palladium(II)‐catalyzed C H activation/oxidative cyclization by the 6‐endo mode is reported for the synthesis of 3‐substituted phosphaisocoumarins from the reaction of arylphosphonic acids with unactivated alkenes under aerobic conditions. Also, α,α‐disubstituted benzylphosphonic acids were phosphaannulated with unactivated alkenes, producing phosphaisochromanones having (Z)‐alkylidenyl groups via anti‐phosphoryloxypalladation by the 6‐exo mode.
992.
Bong Mo Park Kenji Kitamura Yasunori Furukawa Yangyang Ji 《Journal of the American Ceramic Society》1997,80(10):2689-2692
The relationships between cracking and mechanical twinning, and between ferroelectric polarization and mechanical twinning, in stoichiometric LiNbO3 were investigated in the present study. Three sets of mechanical twins crossed one another, and the crossed points of those twins provided preferred sites for the nucleation of cracks. Mechanical twins of LiNbO3 revealed a head-to-tail arrangement of ferroelectric polarization, and complicated polarization states were observed at the crossed points. Some possible mechanisms of crack nucleation and propagation are proposed in this paper. 相似文献
993.
Hong Kyu Park Do Kyung Kim Chong Hee Kim 《Journal of the American Ceramic Society》1997,80(3):743-749
Titania powders were synthesized by the thermal hydrolysis of titanium tetrachloride with the yield of above 85% in a mixed solvent of n -propanol and water. The morphology of the precipitates was controlled by adjusting the volume ratio of n -propanol to water (RH ratio) of the mixed solvent. Precipitates obtained with an RH ratio of 0 were fine, and highly agglomerated. In contrast, an RH ratio of 3 resulted in precipitates consisting of uniform and discrete particles. According to observations of the zeta potentials of precipitates and the dielectric constants of solvents, the discrete particles obtained with an RH ratio of 3 resulted from the low zeta potential and dielectric constant. The result of Fourier transform infrared (FTIR) spectroscopy showed the chemical interaction of particle surface with the solvent alcohol, which decreased the zeta potential of precipitates with an increase of RH ratio. Adding hydroxypropyl cellulose (HPC) as a steric dispersant made it possible to reduce the size of particles to the submicrometer range. Effects of the solvent on the formation and morphology of the resulting particles were investigated. 相似文献
994.
Seong-Soo Hong Gun-Dae Lee Jong-Won Park Dae-Won Park Kyung-Mok Cho Kwang-Jung Oh 《Korean Journal of Chemical Engineering》1997,14(6):491-497
In the present work, we have investigated the reduction of NO by propane over perovskite-type oxides prepared by malic acid
method. The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxides.
In addition, the reaction conditions, such as temperature, O2 concentration, and space velocity have been varied to understand their effects on the catalytic performance. In the LaCoO3 type catalyst, the partial substitution of Ba and Sr into A site enhanced the catalytic activity in the reduction of NO.
For the La0.6Ba (Sr)o.4 Co1−x
FexO3 (x=0-1.0) catalyst, the partial substitution of Fe into B site enhanced the conversion of NO, but excess amount of Fe decreased
the conversion of NO. The surface area and catalytic activity of perovskite catalysts prepared by malic acid method showed
higher values than those of solid reaction method. The conversion of NO increased with increasing O2 concentration and contact time. The introduction of water into reactant feed decreased the catalytic activity but the deactivation
was shown to be reversible over La0.6Ba0.4Co1−x
,FexO3 catalyst. 相似文献
995.
An investigation has been performed of the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms. These materials were foamed in extrusion with the two blowing agents, CO2 and isopentane. The cell density generally increased with an increased content of the blowing agent, for both CO2 and isopentane. The effect of processing pressure on the cell density was distinct when CO2 was used, whereas no pressure effect was observed in the foam processing with isopentane. The cell morphologies for the two PPs were found to be significantly different. A slightly lower nuclei density was observed in the branched PP foams than in the linear PP foams. However, the phenomenon of cell coalescence was observed much less in the branched PP foams. Most cells in the branched PP foams were closed, whereas in the linear PP foams they were connected to each other. The experimental results indicated that the branched structure played an important role in determining the cell morphologies through its effects on the melt strength and/or melt elasticity. 相似文献
996.
Effects of various additives, such as diatomaceous earth, inorganic adsorbent, and polymeric flocculant, on cake filtration
performance were evaluated. By performing the standard vacuum filtration experiments under a constant pressure condition,
we quantified their ability to reduce cake compressibility and to remove fine particulate matters. From the flux decline curves
obtained, we used modified Ruth equation to determine the cake compressibility index. The filtrate clarity was quantified
by measuring its turbidity spectrophotometrically. Diatomaceous earth filter aid was very effective in reducing the compressibility
thereby improving filtrate flux. Calcium phosphate adsorbent was more effective in clarity improvement than in flux enhancement,
whereas an anionic flocculant was effective in both aspects. When these additives were used together, the expected additive,
synergic effect was not realized. However, about 3.5 times higher initial flux and 6-fold improved clarity were obtained as
compared to the control experiment. Experimentally obtained flux decline curves were perfectly fitted into one of the Hermia’s
blocking filtration law equations. Also, it was experimentally observed that the compressibility reduction improved filtrate
clarity in a linear fashion. This type of approach is useful to quantitatively determine each additive’s characteristics and
thus to maximize the performance of cake filtration operations. 相似文献
997.
Dong Hyun Cho Young Gul Kim Moon Jo Chung Jong Shik Chung 《Korean Journal of Chemical Engineering》1997,14(6):502-506
Catalytic fluorination of HCFC-133a was performed over metal oxide catalysts. Chromium oxide showed the best catalytic activity
among several metal oxides tested. An increase in the crystallinity with decreased surface area resulted in a decrease of
catalytic activity for the fluorination reaction. Active phase of chromia is Cr-O-F-OH having a proper ratio of O/F and a
high hydroxyl content. The hydroxyl content on the catalyst is strongly dependent on support material. The selectivity to
HFC-134a is independent of the O/F ratio on the Cr surface. 相似文献
998.
The cloud point curves for polysulfone (PSf)/solvent/water systems were determined by a titration method. A small amount of water was needed to induce liquid-liquid demixing and the temperature effect was small. From numerical calculations, it was found that the binary interaction parameters for the PSf/solvent/water system enlarges the homogeneous region in the phase diagram with a smaller nonsolvent-polymer interaction parameter χ13, a greater nonsolvent-solvent interaction parameter χ12, and a smaller solvent-polymer interaction parameter χ23 and the effect of polymer molecular weight was negligible except in the range of low molecular weight. The phase diagrams, calculated with constant χ12 that was chosen from the concentration-dependent interaction parameter g12 value of the concentration range, were similar to the results obtained with g12. The slope of the tie lines indicated that demixing of the ternary system occurred at relatively similar nonsolvent concentration in both phases. A value of 2.7 for the water-PSf interaction parameter was obtained by fitting the experimental cloud point curve with the calculated binodal lines. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2643–2653, 1997 相似文献
999.
1000.
Separation of guanine and cytosine base pairs in nucleotide is an interesting topic for investigation of DNA structure. Therefore, an understanding of nucleotide separation by chromatography is necessary to prepare DNA molecules. Guanine and cytosine separation in SMB was simulated by Aspen chromatography and it was experimented by assembled 3-zone simulated moving bed (SMB) with change of stream flow rates, sample concentration, and desorbent flow rate. The simulation of batch chromatography was also confirmed by HPLC experiments. Based on these, good operating conditions of SMB chromatography were determined. Three-zone SMB equipment was set up by connecting three C18-HPLC columns, four HPLC pumps, and six multiposition valves. Batch chromatography of cytosine and guanine was conducted to determine the isotherms of the two nucleotides. The outlet streams of SMB, raffinate and extract were sampled and analyzed by analytical HPLC system. The adsorption isotherms of cytosine and guanine were HC= 0.5 and H G =1.05. The highest experimental purity of cytosine and guanine in SMB was obtained as 94.9% and 89.8% with operating parameters of Q feed =0.2 mL/min, Q desorbent =0.6 mL/min, Q extract =0.2 mL/min, Q raffinate =0.6 mL/min, and switching time=7 min. 相似文献