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991.
992.
In the paper, Ding projective modules and Ding projective complexes are considered. In particular, it is proven that Ding projective complexes are precisely the complexes X for which each Xm is a Ding projective R-module for all m ∈ Z. 相似文献
993.
Zhiyong Jiang Jens Rieger Dieter Lilge Rainer Gehrke Zhihong Li Yongfeng Men 《European Polymer Journal》2010,46(9):1866-13808
The morphological development of melt-drawn transparent high-density polyethylene during heating was investigated employing in-situ synchrotron small-angle X-ray scattering (SAXS) technique. The results confirm that at lower temperatures only meridional scattering peaks aligned perpendicular to the extensional flow direction can be observed, indicating a highly oriented lamellar crystallite structure; whereas at higher temperatures an equatorial streak additional to the layer-like meridional scattering pattern develops, reflecting the presence of shish-kebab-like objects in the specimen under investigation. Upon heating, the average thickness of the kebab crystals remains essentially unaffected below 110 °C, and subsequently the selective melting of the less stable kebabs proceeds yielding thicker layered lamellar crystals. When the temperature is raised to 131 °C, the shish-like formation and the thermally stable kebab crystals melt simultaneously. In addition, the microstructure of the melt-drawn specimen subjected to annealing at elevated temperatures was probed at room temperature. As opposed to the SAXS patterns registered at high temperatures, the SAXS diagram measured after annealing shows no equatorial streak, suggesting that the cylindrical structures could be re-formed. This observation can be explained by assuming that the plate-like kebab crystals with their normal parallel to the stretching direction grow and impinge during cooling to room temperature due to secondary crystallization, which can be verified by in-situ SAXS experiments during annealing and subsequent cooling. 相似文献
994.
GuiLing Zhang HongLiang Yuan Hui Zhang Yan Shang Miao Sun Bo Liu ZeSheng Li 《中国科学:化学(英文版)》2010,53(12):2571-2580
The transport mechanisms of four σ-conjugated systems were comparatively studied by combining ATK and Gaussian 03 calculations. It was found that the charge-doped oligosilane behaved in a different way from the boron doped and phosphorus doped oligosilanes in terms of the transmission property. The charge-doped oligosilane showed almost no conductivity owing to the damage of the electron transfer path by charge-doping. By contrast, the boron doped and phosphorus doped oligosilanes were demonstrated to be good semiconductors and NDR behavior was observed for them. This is a reasonable result after the analysis of the transmission spectra, MPSH states, energy gap, conjugation effect, and scattering effect. 相似文献
995.
Pei Hua Shang Chang Mei Cheng Hua Wang Hong Chao Zheng Yu Fen Zhao Key Laboratory of Phosphorus Chemical Biology the Ministry of Education 《中国化学快报》2010,(2)
<正>An efficient and novel method for synthesizing 3′,5′-dithio-2′-deoxyguanosine was described.In this method normal guanosine was used as the starting material.A very efficient procedure was used to synthesize 2-O-tosylguanosine 1,which used 0.1 eq.DBTO instead of 2 eq.1 was treated with LTBH to give 9-(2-deoxy-β-D-threo-pentofuranosyl)guanine 2.2 could be easily turned to the target compound. 相似文献
996.
Guo Xiaoguang Shang Jianpeng Li Jian Wang Liguo Ma Yubo Shi Feng Deng Youquan 《中国化学》2010,28(2):164-170
A series of silica gel immobilized lanthanum catalysts were prepared for the atom‐economy synthesis of N‐substituted carbamates from urea derivatives and dimethyl carbonate. The La/SiO2 catalysts with lanthanum loadings varied from 1.3 wt% to 8.5 wt% were characterized by AES, BET, XRD, TEM, FT‐IR, XPS and TPD. According to the characterization, lanthanum species with particle sizes of 5–10 nm on the surface of silica gel were formed. The catalysts were all amorphous and the surface areas were 336.5–530.2 m2/g. NH3‐TPD analysis showed that all samples exhibited similar acid strength with different acid amounts. FT‐IR measurement indicated that the component of lanthanum species on the catalyst surface were La(OH)3, LaOOH and hydrated La2O3. Also, the peak value of the absolute amount of LaOOH was obtained with 4.3 wt% lanthanum loading. The BET surface area decreased dramatically when the lanthanum loading was above 4.3 wt%. In consideration of the results obtained from the catalytic reactions, it could be concluded that LaOOH was the possible active species and high surface area was important for the high catalytic activity. 相似文献
997.
The cobalt(III) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(II) solutions containing Ti(IV), generating nearly linear (zero-order) profiles that become curved only during the last few percent of reaction. Other Co(III)-Ti(II) systems exhibit the usual exponential traces with rates proportional to [Co(III)]. Observed kinetics of the biphasic catalyzed Ti(II)-Co(III)Br and Ti(II)-Co(III)I reactions support the reaction sequence: [Ti(II)(H20)n]2+ + [Ti(IV)F5]- (k1)<==>(k -1) [Ti(II)(H2O)(n-1)]2+ + [(H2O)Ti(IV)F5]-, [Ti(II)(H2O)(n-1)]2+ + Co(III) (k2)--> Ti(III) + Co(II) with rates determined mainly by the slow Ti(IV)-Ti(II) ligand exchange (k1 = 9 x 10(-3) M(-1) s(-1) at 22 degrees C). Computer simulations of the catalyzed Ti(II)-Co(III) reaction in perchlorate-triflate media yield relative rates for reduction by the proposed active [Ti(II)(H2O)(n-1)]2+ intermediate; k(Br)/k(I) = 8. 相似文献
998.
一类非线性波动方程的势对称分类 总被引:1,自引:0,他引:1
先给出了含有一个任意函数的线性波动方程的古典和势对称的完全分类.然后,在此基础上给出了含有两个任意函数的一类非线性波动方程的两种情形势对称分类,得到了该方程的新势对称.在处理对称群分类问题的难点-求解确定方程组时我们提出了微分形式吴方法算法,克服了以往难于处理的困难.在整个计算过程中反复使用了吴方法,吴方法起到了关键的作用. 相似文献
999.
采用矢量场模型,对具有诱人应用前景的圆柱形垂直腔面发射半导体激光器(VCSEL)的模式阈值增益进行了数值模拟;为减弱金属圆柱的反射以使理论计算更接近实际,采用两种方案,将外加金属包壳视为非理想导体,或在此基础上,将金属包壳与激光器主体结构隔开. 从模式的阈值增益与顶Bragg反射镜层周期数的关系方面,与理想金属外包壳情况进行了比较. 结果表明,高阶贝塞耳函数模式的阈值增益变化规律基本相同,而0阶贝塞耳函数模式的阈值增益变化规律相差较大. 相似文献
1000.