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991.
992.
JunGU MengZHANG DaLiYIN JiYuGUO XiaoTianLIANG 《中国化学快报》2005,16(4):427-429
Microwave-assisted allylic oxidation at C-13 position of 14-deoxysinenxan A was described. This new method (150℃/10 min/5 bar on microwave synthesizer) led to a better yield of compound 1 and shorter reaction time. 相似文献
993.
994.
Let G be finite group and let S be a subset of G. We prove a necessary and sufficient condition for the Cayley digraph X(G, S) to be primitive when S contains the central elements of G. As an immediate consequence we obtain that a Cayley digraph X(G, S) on an Abelian group is primitive if and only if S−1S is a generating set for G. Moreover, it is shown that if a Cayley digraph X(G, S) on an Abelian group is primitive, then its exponent either is
or is not exceeding
. Finally, we also characterize those Cayley digraphs on Abelian groups with exponent
. In particular, we generalize a number of well-known results for the primitive circulant matrices. 相似文献
995.
996.
The solid state reaction of 3-methyl-1-phenyl-5-pyrazolon(eM PP) with aromatic aldehydes and ketones, benzil derivatives and
imides, and the solid state Michael addition reaction of MPP with 4-arylidene-3-methyl-lphenyl-5-pyrazolone2 were investigated. Some new solid state reactions between the reactants were found, from which a series of new compounds
were obtained. The structures of the products were identified by IR,1H NMR, MS, elemental analyses and also by X-ray crystal analysis, and the reaction mechanism of MPP with aromatic aldehydes
and ketones was proposed.
Project supported by the National Natural Science Foundation of China. 相似文献
997.
Nonlinear responses of a rub-impact overhung rotor 总被引:1,自引:0,他引:1
For a rotor system with bearings and step-diameter shaft in the oxygen pump of an engine, the contact between the rotor and the case is considered, and the chaotic response and bifurcation are investigated. The system is divided into elements of elastic support, shaft and disk, and based on the transfer matrix method, the motion equation of the system is derived, and solved by Newmark integration method. It is found that hardening the support can delay the occurrence of chaos. When rubbing begins, the grazing bifurcation will cause periodic motion to become quasi-period. With variation of system parameters, such as rotating speed, imbalance and external damping, chaotic response can be observed, along with other complex dynamics such as period- doubling bifurcation and torus bifurcation in the response. 相似文献
998.
The influence of the oxygen partial pressure on the properties of indium tin oxide films deposited by rf reactive magnetron sputtering has been studied. The oxygen partial pressure was varied from 3.2 × 10−4 to 1.0 × 10−3 mbar. It has been found that the 4 × 10−4 mbar of oxygen partial pressure is a critical point. When the oxygen partial pressure is lower than 4 × 10−4 mbar, the deposition rate of the films is high; the films have low transmittance and electrical resistivity; the X-ray diffraction shows that the films have a random orientation and the images of the scanning electron microscopy show that the films surface are smooth without structure. When the pressure is higher than 4 × 10−4 mbar, the deposition rate is low and does not change as the oxygen partial pressure is further increased; the transmittance and the electrical resistivity are both high; the films show the preferred orientation along the (440) direction; the films surface show a clear structure and as the pressure is increased further, the films become porous. Considering both the factor of transmittance and resistivity, the optimum oxygen partial pressure will be 3.6 × 10−4 mbar. The films prepared at this pressure have 80% transmittance and 9 × 10−4 Ω cm resistivity. 相似文献
999.
针对应用RTP的大规模会话,提出了改进的RTCP传输间隔算法,并对改进算法和现行算法进行了模拟和分析,结果表明改进算法有效地减小了因大量用户同时加入而导致的RTCP包发送间隔误差,缓解了大规模会话初始时RTCP包造成的拥塞. 相似文献
1000.
A series of siloxane-based liquid crystalline elastomers containing biphenyl benzoate mesogenic units and ionic Brilliant Yellow moieties was synthesized. The chemical structures and liquid crystalline properties of the samples were characterized by FTIR, 1H NMR, DSC, POM and XRD. The effective crosslink density of the ionic elastomers was determined by swelling experiments in organic/buffer mixtures. All the polymers displayed a smectic mesophase. It was shown that the glass transition and melting point temperatures of the polymers increased slightly with increasing content of ionic and mesogenic groups in the polymers, while the liquid crystal mesophase region decrease slightly. 相似文献