基于遗传神经算法的压力钢管外压稳定性分析

压力钢管外压稳定性分析是重要而难以解决的问题。用遗传-神经网络模型对压力钢管外压稳定问题进行仿真计算,模型具有神经网络强大的函数逼近功能,同时利用遗传算法克服传统神经网络方法易陷入局部极小点的缺陷。实例仿真结果表明,用实数编码遗传神经网络模型分析加劲压力钢管的外压稳定性,具有效率高、鲁棒性好的优点,精度满足工程要求。     

Genetic diversity and haplotype structure of 24 Y‐chromosomal STR in Chinese Hui ethnic group and its genetic relationships with other populations

In the present study, 24 Y‐chromosomal short tandem repeat (Y‐STR) loci were analyzed in 115 unrelated Hui male individuals from Haiyuan county or Tongxin county, Ningxia Hui Autonomous Region, China, to evaluate the forensic application of the 24 STR loci and to analyze interpopulation differentiations by making comparisons between the Hui group data and previously published data of other 13 populations. A total of 115 different haplotypes were observed on these 24 Y‐STR loci. The gene diversities ranged from 0.4049 (DYS437) to 0.9729 (DYS385a, b). The overall haplotype diversity was 1 at AGCU 24 Y‐STR loci level, while the values were reduced to 0.999237, 0.996949, and 0.996644 at the Y‐filer 17 loci, 11 Y‐STR loci of extended haplotype and 9 Y‐STR loci of minimal haplotype levels, respectively; whereas, haplotype diversity for additional 7 loci (not included in Y‐filer 17 loci) was 0.995271. The pairwise F_ST, multidimensional scaling plot and neighbor‐joining tree indicated the Hui group had the closest genetic relationship with Sala in the paternal lineage in the present study. In summary, the results in our study indicated the 24 Y‐STRs had a high level of polymorphism in Hui group and hence could be a powerful tool for forensic application and population genetic study.     

Structural polymorphism analysis of Chinese Mongolian ethnic group revealed by a new STR panel: Genetic relationship to other groups

Mongolian is the eighth largest ethnic minority on Chinese population data according to the 2010 census. In the present study, we presented the first report about the allelic frequencies and forensic statistical parameters at the 21 new STRs and analyzed linkage disequilibrium of pairwise loci in the Mongolian ethnic minority, China. Hardy–Weinberg equilibrium tests demonstrated no significant deviations except for the D1S1627 locus. The cumulative power of discrimination and power of exclusion of all the loci are 0.9999999999999999992576 and 0.9999997528, respectively. The results of analysis of molecular variance showed that significant differences between the Mongolian and the other eight populations were found at 1‐9 STR loci. In population genetics, the results of principal component analysis, structure analysis, and phylogenetic reconstruction analysis indicated shorter genetic distance between the Mongolian group and the Ningxia Han. All the results suggest that the 21 new STR loci will contribute to Chinese population genetics and forensic caseworks in the Mongolian group.     

High-Curvature Transition-Metal Chalcogenide Nanostructures with a Pronounced Proximity Effect Enable Fast and Selective CO2 Electroreduction

A considerable challenge in the conversion of carbon dioxide into useful fuels comes from the activation of CO₂ to CO₂^.− or other intermediates, which often requires precious-metal catalysts, high overpotentials, and/or electrolyte additives (e.g., ionic liquids). We report a microwave heating strategy for synthesizing a transition-metal chalcogenide nanostructure that efficiently catalyzes CO₂ electroreduction to carbon monoxide (CO). We found that the cadmium sulfide (CdS) nanoneedle arrays exhibit an unprecedented current density of 212 mA cm⁻² with 95.5±4.0 % CO Faraday efficiency at −1.2 V versus a reversible hydrogen electrode (RHE; without iR correction). Experimental and computational studies show that the high-curvature CdS nanostructured catalyst has a pronounced proximity effect which gives rise to large electric field enhancement, which can concentrate alkali-metal cations resulting in the enhanced CO₂ electroreduction efficiency.     

Syntheses of nucleosides with a 1′,2′-β-lactam moiety as potential inhibitors of hepatitis C virus NS5B polymerase

To discover novel nucleosides as potential anti-HCV agents, nucleosides with a 1′,2′-β-lactam moiety were designed as a hybrid scaffold of MK-608 and GS-6620. Synthetic strategies were successfully developed to prepare two series of C-nucleosides with a 1′,2′-β-lactam moiety: a 7-deaza-purine C-nucleoside analog 11 was prepared in 10 steps with an overall yield of 3.7%; a purine C-nucleoside analog 22 was prepared in 9 steps with an overall yield of 9.7%.     

Nanocarbons: Opening New Possibilities for Nano-engineered Novel Catalysts and Catalytic Electrodes

Nanocarbons find increasing relevance for the development of advanced, sometimes radically new, catalysts and catalytic electrodes. This perspective contribution discusses the potential of nanocarbons as a new class of catalytic materials, even if carbons (in the form mainly of active carbon materials) are already extensively applied as supports for catalysts. The control of nano-dimension and the improved understanding in tailoring the surface reactivity open new possibilities for their nano-engineering and the development of novel catalytic materials. With focus on the nature of the active sites in nanocarbon catalysts, we discuss here some of the novel possibilities opened by these materials to address the new challenges for catalysis deriving from moving to a more sustainable chemical and energy production.     

Mechanistic Origin of Chemoselectivity in Thiolate‐Catalyzed Tishchenko Reactions

The thiolate‐catalyzed Tishchenko reaction has shown high chemoselectivity for the formation of double aromatic‐substituted esters. In the present study, the detailed reaction mechanism and, in particular, the origin of the observed high chemoselectivity, have been studied with DFT calculations. The catalytic cycle mainly consisted of three steps: 1,2‐addition, hydride transfer, and acyl transfer steps. The calculation results reproduce the experimental observations that 4‐chlorobenzaldehyde acts as the hydrogen donor (carbonyl part in the ester product), while 2‐methoxybenzaldehyde acts as the hydrogen acceptor (alcohol part in the product). The two main factors are responsible for such chemoselectivity: 1) in the rate‐determining hydride transfer step, the para‐chloride substituent facilitates the hydride‐donating process by weakening the steric hindrance, and 2) the ortho‐methoxy substituent facilitates the hydride‐accepting process by stabilizing the magnesium center (by compensating for the electron deficiency).     

Accurate Prediction of Au?P Bond Strengths by Density Functional Theory Methods

The recent development of Au‐catalyzed reactions has greatly enriched the methods of organic synthesis. The phosphine or phosphate‐coordinated Au complexes have shown high efficiency in catalyzing various C? C and C? H activations. In many of these reactions, the Au? P bond strength was found to play an important role in determining the catalytic efficiency. In the present study, the accuracy of different theoretical methods for prediction of Au? P strengths has been examined on basis of the experimental enthalpy changes between different ClAu(PR₃) and ClAu(THT) (THT=tetrahydrothiophene). By comparing the different DFT functionals (e.g. B3LYP, TPSS, M06), different basis sets (including the different effective core potentials on Au and the total electron basis sets on all other atoms), and different solution phase single point calculations, we found that the TPSS/(CPE‐121G+f:6‐311+G(d,p)(SMD)//TPSS/(CPE‐121G:6‐31G(d) ( M1 ) method gives the best correlations with the available experimental results. Meanwhile, the calculations with B3LYP//TPSS and M05//TPSS also give comparable calculation results. Finally, the specified method ( M1 ) is used to calculate the Au? P bond dissociation enthalpies and energies of different ClAu(PR₃)/ClAu(P(OR)₃) complexes. By accurately reproducing the available experimental results, we believe that the method ( M1 ) is reliable for the theoretical analysis of Au‐P systems.     

硅烷类外给电子体的取代基变化对丙烯聚合影响的研究

合成了2种新型硅烷化合物双环己基二甲氧基硅烷(Donor-H)、双哌啶二甲氧基硅烷(Donor-Py),将其与工业化的环己基甲基二甲氧基硅烷(Donor-C)分别作为外给电子体,用于MgCl2负载的Ziegler-Natta催化剂催化丙烯聚合,通过DSC、GPC、SSA和13C-NMR等分析手段研究了3种外给电子体取代基的变化对催化剂的催化活性、氢调敏感性、聚丙烯的等规度、分子量分布、结晶能力、等规序列分布的影响.结果表明,随着外给电子体取代基体积的增大,外给电子体的给电子能力逐渐增强.与Donor-C相比,随着外给电子体取代基体积的增大,合成的具有较大取代基的Donor-H和Donor-Py用于丙烯聚合时都表现优异的催化性能,特别是新型含有N杂原子的氨基硅烷类Donor-Py为外给电子体的催化剂的催化活性和制备的聚丙烯的等规度最高,聚丙烯的熔融指数可调范围最宽,结晶能力更强.氨基硅烷类Donor-Py制备的聚丙烯SSA热分级后的高等规组分含量最多,可高达64.5%,聚丙烯等规序列长度最长,聚丙烯的等规序列分布最窄,而且13C-NMR结果也表明聚丙烯等规序列长度MSL最长,聚丙烯的分子链最规整.     

Modification of Rubber by Cardanol-Formaldehyde Resins and Epoxidized Cardanol

Abstract

Cardanol-formaldehyde resin (CF) and cardanol glycidylether (CGE) have been synthesized for reinforcing natural rubber (NR), a blend of NR and styrene-butadiene rubber (SBR), and nitrile-butadiene rubber (NBR). The novolac CF resin reinforced the NR, SBR, and NBR. The resolic CF is not only a reinforcing agent but also a hardener (crosslinking agent) for NBR by means of the methylol groups of CF with the CN- group of NBR. The CGE resin was synthesized by the epoxidation of cardanol by epichlorohydrin; it could be used as a reinforcing agent for NR and for crosslinking maleinized NR. The results of estimates of the physical properties of the vulcanisate, their DSC diagrams, and SEM showed the enhanced properties of the final products.