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901.
本文利用假设剪切应和薄膜应变场的新型退化壳单元,并考虑大应主影响对壳体结构弹塑性动态分析进行了研究,并编制了相应的程度,此程序采用修正的Lagrangian公式,它不仅考虑了大变形大应变的影响,还对单元的节点坐标和厚度在每个时间步后都给予修正,通过对一些算例计算表明,此程序数值精度很好,可用于壳体结构的工程分析,并得出结论,对于应变问题考虑和忽略大应变影响将有较大的不同。 相似文献
902.
冲击伤复合高速破片致伤的损伤特点和冲击伤防护研究 总被引:17,自引:0,他引:17
探讨了冲击伤复合高速破片致伤的损伤特点及复合材料对冲击伤的防护效果。结果表明,肢体高速破片致伤对肺冲击伤具有加重作用,加重效应主要发生在原发冲击伤部位,加重效应的机理可能与压力波引起的血流扰动有关。利用复合材料防护可减轻肺冲击伤程度,降低动物的死亡率。 相似文献
903.
904.
考虑双层碳纳米管的层间范德华力,采用连续介质力学的波动理论,建立了双层碳纳米管中周向导波传播模型,研究周向导波的频散现象.通过与单层碳纳米管结果的比较表明,双层碳纳米管中周向导波的传播表现出更为明显的频散特性,出现更多的模态干涉现象,并发现在某些特殊频率处出现成对模态的消失与新启现象. 相似文献
905.
梁的动力稳定性分析的有限元方法 总被引:6,自引:0,他引:6
提出了对梁进行动力学稳定性分析的有限元方法──给出了单元质量矩阵,抗弯刚度矩阵,几何刚度矩阵及相应的Mathieu方程,通过坐标变换消除了方程的动力与静力耦合,然后说明了由这种具有参数激励耦合的多自由度系统的Mathieu方程求得系统一般参数共振及组合参数共振的过渡曲线的约束参数方法与多尺度方法。最后作为算例求出了均匀简支梁受简谐轴向力作用时的过渡曲线。 相似文献
906.
907.
Regioselective Acceptorless Dehydrogenative Coupling of N‐Heterocycles toward Functionalized Quinolines,Phenanthrolines, and Indoles
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Dinesh Talwar Angela Gonzalez‐de‐Castro Dr. Ho Yin Li Prof. Jianliang Xiao 《Angewandte Chemie (International ed. in English)》2015,54(17):5223-5227
A new strategy has been developed for the oxidant‐ and base‐free dehydrogenative coupling of N‐heterocycles at mild conditions. Under the action of an iridium catalyst, N‐heterocycles undergo multiple sp3 C? H activation steps, generating a nucleophilic enamine that reacts in situ with various electrophiles to give highly functionalized products. The dehydrogenative coupling can be cascaded with Friedel–Crafts addition, resulting in a double functionalization of the N‐heterocycles. 相似文献
908.
Epigenetic Genome Mining of an Endophytic Fungus Leads to the Pleiotropic Biosynthesis of Natural Products
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Dr. Xu‐Ming Mao Dr. Wei Xu Dr. Dehai Li Dr. Wen‐Bing Yin Dr. Yit‐Heng Chooi Dr. Yong‐Quan Li Dr. Yi Tang Dr. Youcai Hu 《Angewandte Chemie (International ed. in English)》2015,54(26):7592-7596
The small‐molecule biosynthetic potential of most filamentous fungi has remained largely unexplored and represents an attractive source for the discovery of new compounds. Genome sequencing of Calcarisporium arbuscula, a mushroom‐endophytic fungus, revealed 68 core genes that are involved in natural product biosynthesis. This is in sharp contrast to the predominant production of the ATPase inhibitors aurovertin B and D in the wild‐type fungus. Inactivation of a histone H3 deacetylase led to pleiotropic activation and overexpression of more than 75 % of the biosynthetic genes. Sampling of the overproduced compounds led to the isolation of ten compounds of which four contained new structures, including the cyclic peptides arbumycin and arbumelin, the diterpenoid arbuscullic acid A, and the meroterpenoid arbuscullic acid B. Such epigenetic modifications therefore provide a rapid and global approach to mine the chemical diversity of endophytic fungi. 相似文献
909.
Fabrication and performance of microencapsulated phase change materials with hybrid shell by in situ polymerization in Pickering emulsion
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Microencapsulated phase change materials (MePCMs) using melamine–formaldehyde resin/SiO2 as shell were investigated in this paper. Organically modified SiO2 particles were employed to stabilize Pickering emulsion, and in situ polymerization of melamine and formaldehyde was carried out to form hybrid shell. The performances of resultant MePCMs with hybrid shell were investigated comparatively with the MePCMs with polymer shell. SiO2 particles raise the microencapsulation efficiency by improving the stability of emulsion and providing a precipitation site for melamine–formaldehyde resin. Also, the mechanical strength, thermal reliability, and anti‐osmosis performance of MePCMs were improved significantly by SiO2 particles in the shell. Our study shows that Pickering emulsion is a simple and robust template for MePCMs with polymer‐inorganic hybrid shell. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
910.
Effects of GC temperature and carrier gas flow rate on on‐line oxygen isotope measurement as studied by on‐column CO injection
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Although deemed important to δ18O measurement by on‐line high‐temperature conversion techniques, how the GC conditions affect δ18O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO–N2 mix onto the GC column by a six‐port valve and examined the CO yield, CO peak shape, CO–N2 separation, and δ18O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N2 and CO decreases with an increase of GC temperature and carrier gas flow rate. δ18O value decreases with the increase of CO injection volume (when half m/z 28 intensity is <3 V) and GC temperature but is insensitive to carrier gas flow rate. On average, the δ18O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ18O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C16O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N2–CO separation, lower He consumption, and insignificant effect on δ18O value, while a higher‐than‐60 °C GC temperature and a larger‐than‐100 µl CO volume is also recommended. When no N2 peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献