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891.
将联想思维过程抽象成联想图,该图是以变量之间的相关性和条件相关性表示的正态分布,进而讨论了联想图的可树型分解问题,包括可树型分解条件及其树重构算法,可树形分解的联想思维不仅是发散的,而且是递进的,因而具有更高的创造性,这些结论不仅可用于评价人类的联想思维过程,而且可通过对联想思维过程重构来刺激创造性思维的产生。 相似文献
892.
对层状半空间弹性参数的反演这一具有较强的工程应用价值的问题进行了研究。先通过引入共轭波函数给出了泛函导数的表达式,然后构造一均方误差函娄把反演问题转化为寻求最优解,并通过共轭梯度法导出了非线性迭代公式,最后进行了数值计算。数值计算结果表明,该公式具有较好的收敛性和稳定性。 相似文献
893.
欧代永 《重庆邮电学院学报(自然科学版)》2002,14(1):82-83
基于Infranet的网上支付系统就是Internet用户使用信用卡在网上直接将网络使用费划到ISP的账户上。分析了基于Infranet软件的网上支付系统的体系结构并给出了系统处理流程。 相似文献
894.
Previous investigations have shown that nifA gene is involved in nodulation and symbiotic nitrogen fixation regulation of Rhizobium. We study the role of nifA on nodulation of leguminous plants. We found that Sinorhizobium fredii harboring multi-copy plasmid carrying the constitutively expressed Klebsiella pneumoniae nifA exhibited an increase of noduiation activity and nodulation competitiveness on soybean plants. The Nod-factor secreted by the rhizobia cells containing the multi-copied nifA was assayed,and preliminary results showed that S. fredii containing the multi-copy plasmid carrying nifA produced higher strength of Nod-factor than the rhizobia containing the same plasmid carrying the vector did. 相似文献
895.
Xinhua Dai Xicheng Ai Zhimin Liu Mingjun Yang Guangying Yang Buxing Han Jian Xu Xianmin Zhang Xin Wu 《科学通报(英文版)》2002,47(12):982-985
A focusing method is developed to characterize the refractive index profile of polymer optical fiber (POF). Based on the refractive index profile the theoretical bandwidth and the core index exponentα (α > 0) of POF are calculated. The results show that the value of theoretical bandwidth agrees well with the experimental data. 相似文献
896.
Since the beginning of the 1980s, Dai Qianhuan predicted based upon his di-region theory that the carcinogenesis switched
on by the so-called physical carcinogenic factors including radiation, asbestos and foreign matter implantation, is just initiated
through the cross-linking between DNA complementary pair bases induced by them. In this note, it was evidenced with the DNA
filter elution method that the oxygenase activated by asbestos induces the cross-linking between DNA inter-strands and DNA-protein
with dosage correlation, in which over 80% of DNA inter-strand cross-link ratio account for the total cross-link ratio. Obviously,
both of the cross-linkages are just induced by hydroxyl free radical, HO ·, because the ferrous ion increased the cross-link
ratios up to several times through Fenton reaction and vitamin C inhibited the cross-link ratios with factors of 8–9 by destroying
the hydroxyl radical. Non-carcinogen but with lower free radical formation energy, pyrene, by culturing with asbestos gave
3–4 times cross-link ratios than the original ratios induced by asbestos only. Estradiol, an endogenous carcinogen, as a bio-electrophilic
species but with higher free radical formation energy by culturing with asbestos, gave only 1.2 time cross-link ratios than
expected ones. Ferrous ion which can increase HO · concentration through Fenton reaction, increased the ratios to 2–2.5 times
in the former case but only 1.2 time in the latter case. Vitamin C, a free radical scavenger, gave a powerful inhibition to
the cross-linking with a factor of 8–11 in the former case but a weak inhibition with a factor of 1.2 only in the latter case.
So, it is evidenced further that the cross-linkages induced by asbestos are originated from hydroxyl radical. Reasonable structures
of the cross-linking products induced by asbestos or hydroxyl radical have been depicted based upon AMI MO theory. These structures
have been verified further by a reasonable explanation of the mutational spectrum induced by hydroxyl radical. 相似文献
897.
Interaction of hepatitis B virus with tumor suppressor gene p53: its significance and biological function 总被引:2,自引:0,他引:2
The mechanism of the interaction of hepatitis B virus (HBV) with tumor suppressor p53 and its role in the hepatocar-cinogenesis have been studied by PCR-directed sequencing, gel shift assays and in situ ultraviolet cross-linking assay. The biological function of the interaction of HBV with p53 gene was investigated by co-transfection of chloramphenicol acetyltransferase ( CAT) reporter gene. p53 and HBV DNA. and quantitative PCR. Among the 16 primary hepatocellular carcinoma (PHC) samples. 13 were HBV-DNA positive. 10 HBxAg positive and 9 p53 protein positive. The p53 gene point mutation was found in 5 samples, one of which had a G to T substitution located at codon 249. After analyzing the HBV genome by a computer program, a p53 response element binding sequence was found in HBV genome at upstream of enhancer I. from 1047 to 1059 nucleotides. This sequence could specifically bind to p53 protein, increase p53 protein accumulation in the PHC cells and stimulate the transactivating activity of p53 and HBV replication . The results also revealed that HBxAg could combine with p53 protein to form a complex in the cells and enhance CAT expression. Immunocytochemical staining showed that p53 protein complex was located in the cytoplasm and the process of p53 entry to nuclei was. in part, blocked. From our results, we conclude that the mutation of p53 gene at codon 249 is infrequent in HBV-associated PHC. the DNA-protein binding between HBV and p53. and the protein-protein binding between HBxAg and p53 might lead to the reduction or inactivation of p53 protein, which in turn resulting in HBV-associated hepatocarcinogenesis. 相似文献
899.
用密度泛函理论的DFF/ROB3LYP方法计算了几种一碳掺杂(碳取代一个硼原子或氮原子)的硼氮纳米管的电子结构,研究了其导电性,得到了这种碳掺杂硼氮纳米管的能带结构和态密度曲线,并与纯硼氮纳米管作了比较,讨论了碳掺杂对硼氮纳米管导电性的影响. 相似文献
900.
对2,4-二氨基-5-甲基-6-(取代苯胺基)甲基吡啶[2,3-d]并嘧啶类二氢叶酸还原酶抑制剂进行了定量构效关系的量子化学研究,证明了偶极矩,LUMO能级和HOMO-LUMO能隙对其活性有着重要的影响. 相似文献