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121.
In this paper,large-sized sapphire (230×210 mm,27.5 kg) was grown by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center). Dislocation peculiarity in large sapphire boule (0001) basal plane was investigated by chemical etching,scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6×101~8.0×102 cm-2,in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally,the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method. 相似文献
122.
自1960年Hoffman等提出聚合物结晶成核理论以来,人们对聚合物结晶生长速率、片晶的侧向尺寸随过冷度的变化等现象成功地进行了理论描述.1997年,Hoffman等对聚合物结晶成核理论进行修正,将de Gennes的聚合物“蛇行”概念。引入表面成核理论,通过对单根分子链从过冷熔体“卷绕”到晶体前沿所需的时间进行估算,其结果远远低于Flory预言时间约3~5个数量级,据此,Hoff-man认为,在聚合物结晶过程中,分子链在强迫稳态下的“蛇行”运动有足够的时间解缠结和结晶。 相似文献
123.
Haplotypic variation within and among the Ascaris populations representing six provinces in China was investigated. Mitochondrial DNA regions in the cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes were amplified by PCR from total genomic DNA samples (n > 720) from Ascaris individuals from humans and pigs, and subjected to mutation scanning and subsequent selective sequencing. For the cox1, ten different electrophoretic profiles were recorded for human Ascaris, and the same number for pig Ascaris, one of them being common to both host species. For the nad1, 11 different profiles were detected for human Ascaris, and 15 for pig Ascaris. Having defined all haplotypes (20 for pcox1 and 26 for pnad1) by sequencing, their frequencies were estimated in each of the two host species and each of the six provinces. For each mitochondrial region, the frequency of the different haplotypes varied considerably, depending on host species and geographical origin. Analysis of the sequence data (representing all haplotypes for each mitochondrial locus) by F-statistics indicated restricted gene flow between human Ascaris and pig Ascaris, and supported the conclusions from previous molecular epidemiological investigations that pigs are not a significant source of Ascaris infection in humans in endemic regions. 相似文献
124.
具有ZSM-5结构的含钛和含硼分子筛是催化性能良好的新型杂原子分子筛,可分别作为碳氢化合物的氧化反应[1]和制备高纯异丁烯的催化剂[2]。近年来,有关这2种分子筛的合成已见报道[1~4]。但其合成均采用碱性介质,成核和晶化都比较快,因此未能得到生长完美的杂原子ZSM-5型分子筛大单晶。 相似文献
125.
Solid-state nanopore in analytical chemistry has developed rapidly in the 1990s and it is proved to be a versatile new tool for bioanalytical chemistry. This review focuses on the analysis of ions and small molecules with nanopores including nanopipettes, polymer film nanopores, Si3N4 nanopores, graphene nanopores, MoS2 nanopores and MOFs. 相似文献
126.
127.
The crystal structures of pyrene and substituted and complexed derivatives of pyrene have been investigated by X-ray and neutron diffraction. The geometry of the pyrene skeleton has been determined experimentally with high accuracy and calculated by quantum chemical methods. In the cases reported in the literature and cited here the pyrene skeleton has the molecular symmetry mmm or mm2 with values for the bond lengths of the six symmetrically independent bondsa, b, c, d, e, f differing significantly in the limits of error. Mean values of a number of experimental and theoretical bond lengths are given and can be considered as standard values for the mm2 symmetric pyrene skeleton. In the case of substitution of the pyrene in 3-position with a polar heterocyclic molecule of the azomethine-imine type the mm2 symmetry vanishes, a C–H ... N intramolecular hydrogen bond arises and the directly neighbouring pyrene units are not packed parallel with their planes to each other, but they are considerably tilted. Relatively narrow intermolekular C-C contacts, 3.314 and 3.368 Å, have been observed. The conclusion is drawn that the asymmetry of the pyrene molecule and a tilt of directly neighbouring pyrene units in the crystal packing can be induced by substitution e. g. with suitable polar heterocycles.
Juli 1985. 相似文献
128.
本文以1,3-环己二甲胺[1,3-Cyclohexanebis(methylamine), CHBMA]为模板剂, 采用水热法合成了微孔磷酸亚磷酸锌锰 [H2CHBMA][Zn1.5Mn(HPO3)2(PO4)]·H2O(命名为TJPU-3Mn), 单晶结构解析显示该化合物为首个与超大孔磷酸铝JDF-20具有相同拓扑结构的微孔晶体, 沿c方向具有二十元环超大孔道, 孔道中的CHBMA分子均为顺式构象, 有望用于分离和识别CHBMA异构体. 相似文献
129.
采用原子力显微镜的单分子力谱(SMFM)技术研究了多药耐药相关蛋白1(MRP1)与其抗体间的相互作用, 并考察了人舌癌细胞系TCA8113经高剂量平阳霉素(BLM)反复间歇诱导前后细胞表面MRP1的表达差异. 实验结果表明, MRP1与其抗体之间存在特异性相互作用力, 当针尖运动速率为2.5 μm/s时, 作用力大小约为(182±35) pN; 而且药物诱导后MRP1在人舌癌细胞上的表达明显增强. 本工作为了解活细胞水平上MRP1的表达提供了新方法, 有助于肿瘤细胞多药耐药性(MDR)的研究. 相似文献
130.