Origin of the solvent effects on the barrier to amide isomerization from the combined QM/MM Monte Carlo simulations

The origin of the solvent effects on the free energy of activation for the isomerization of N,N-dimethylformamide in water, CHCl₃ and CCl₄ has been investigated through statistical mechanical simulations using the combined quantum mechanical and molecular mechanical AM1/OPLS potential. The differential solvations between the ground state and transition state in various solvents can be attributed to the differences in molecular dipole moments in solution, and to the solvent polarization effects. In polar solvents, DMF is polarized more favorably in the ground state than in the rotated conformers, leading to greater solvent contributions. The modest solvent effects in CCl₄ are a reflection of its much smaller dielectric constant.     

煤的清洁利用技术的现状与发展

文章针对中国一次能源以煤为主的特点,深入分析了几种主要的煤的洁净利用技术的现状及存在的主要问题和发展趋势,其中包括大容量、高参数的超(超)临界燃煤发电技术、燃煤烟气净化技术、循环流化床燃烧技术(CFBC)、整体煤气化联合循环技术(IGCC)和煤的洗选技术.在此基础上,给出了中国煤的清洁利用方式的建议:近期仍以超(超)临界燃煤发电机组+燃煤烟气净化技术和循环流化床燃烧技术为主;整体燃气化联合循环技术、富氧燃烧技术(特别是加压富氧燃烧技术)以及二氧化碳的捕集和封存技术(CCS),具有广阔应用前景,值得长期大力发展.     

Bionomic exploitation of a ratio-dependent predator–prey system

The present article deals with the problem of combined harvesting of a Michaelis–Menten-type ratio-dependent predator–prey system. The problem of determining the optimal harvest policy is solved by invoking Pontryagin's Maximum Principle. Dynamic optimization of the harvest policy is studied by taking the combined harvest effort as a dynamic variable. Computer simulations are carried out to illustrate our analytical findings. Biological and bioeconomical interpretations of the results are explained critically.     

The effect of crystallization behavior on high conductivity,enhanced mechanism and thermal stability of poly(ε-caprolactone)/multi-walled carbon nanotube composites

Poly(ε-caprolactone) (PCL) composites filled by multi-walled carbon nanotubes (MWCNTs) which was non-covalently modified by the combined surfactants of poly(sodium 4-styrenesulfonate) and cetyltrimethyl-ammonium bromide (PSS-CTAB) were fabricated via simple solution precipitation method. PCL/MWCNTs composites provided with the low procolation threshold (0.4?wt%) and high electrical conductivity due to good dispersion of MWCNTs. And the excellent mechanical properties and enhanced thermal stability were also obtained with the addition of modified MWCNTs. In addition, all PCL composites showed significantly enhanced crystallization with increasing the MWCNTs contents, which demonstrated that the MWCNT-induced crystallization of PCL could effectively regulate the properties of composites. In a word, introducing non-covalent functionalized MWCNTs in the polymer system was a promising way for developing excellent conductive composites.     

电絮凝-O3联合工艺处理页岩气压裂采出水

通过研究比较不同处理工艺对页岩气压裂采出水的效果,设计出电絮凝-O_3联合处理采出水的工艺。以化学需氧量(COD)、总悬浮物(TSS)为指标,讨论电絮凝-O_3联合工艺处理页岩气压裂采出水过程中pH、电流密度、电极间距、电解时间以及O_3通气量的影响。结果表明,当pH=8. 0、电流密度为1250A/m~2、极板间距为2cm、电解时间6min、O_3通气量为40L/h时,COD去除率为98. 3%,TSS的去除率为95. 9%,经过电絮凝-O_3联合处理后的采出水的色度、浊度、oil及NH_4-N等污染指标都达到了国家排放标准。     

Flow separation behind a rib in a channel with laminar flow

Visualization data and results of combined measurements of flow quantities in flow with separation past a rib at nominally laminar regime of channel flow are reported. In the separation region, the flow is found to be essentially three-dimensional and unsteady, exhibiting a distinct cellular structure and flow zones with transverse motion. It is shown that the rib-induced flow separation gives rise to low-frequency fluctuations of flow velocity and initiates the turbulence transition in the channel flow. The critical Reynolds number at which flow instability starts developing in the channel is estimated. It is shown that at Reynolds numbers higher than the critical Reynolds number the linear integral scale of flow velocity fluctuations in the channel is defined by the duct size.     

铅基堆超临界CO2复合循环发电系统热力学分析

本文对比了再压缩超临界CO2 (S-CO2)循环、蒸汽朗肯循环、He布雷顿循环分别应用于铅基堆的最优热学性能,明确了S-CO2循环与铅基堆结合较传统循环的热力学优势。为进一步提高再压缩S-CO2循环的效率,以跨临界CO2 (T-CO2)循环为底循环构建了再压缩S-CO2/T-CO2复合循环,探讨了不同顶循环透平入口温度、压力和压缩机入口温度条件下系统性能的变化规律,对比了S-CO2/T-CO2复合循环和S-CO2循环的热学性能。结果表明:铅基堆再压缩S-CO2循环发电系统较传统循环形式具有更高的热效率;构建的S-CO2/T-CO2复合循环能够有效提高S-CO2循环的效率,在所研究参数范围内,S-CO2/T-CO2复合循环的热效率和效率比S-CO2循环分别最大可提高约4.8%和8.3%;再压缩S-CO2循环和S-CO2/T-CO2复合循环热学性能随顶循环关键参数变化规律具有一致性。     

新组合模型在光电功率预测中的应用

为提高光伏预测要求的精准性,文章提出一种新算法将神经网络和ARMA算法改进组合,构成NEW ARMA-BP模型算法.以某30兆瓦的光伏电站采集的输出功率为输入样本,基于ARMA和BP神经网络算法在Matlab环境下依次搭建了相应的预测模型,预估光伏短期输出量.采用"误差正态检验图"判断基于两种不同算法的误差水平,依据两种单模型预测误差,运用所提出的新方法计算权值并获得新的预测值.基于Matlab的仿真结论验证了组合预测在光伏输出预测领域的适用性.     

In vitro antioxidant/prooxidant effects of combined use of flavonoids

The present study was undertaken to investigate the individual and combined antioxidant or prooxidant effects of genistein, daidzein and quercetin in human erythrocytes and rat microsomes in vitro. Their reducing potential against oxidation of a redox sensitive fluorescent probe, their protective effect against H₂O₂-induced membrane lipid peroxidation and their inhibitory effect on AAPH-induced hemolysis were evaluated. Genistein and daidzein were prooxidant in erythrocytes but antioxidant in microsomes where their metabolites might have been formed which suggests the importance of metabolic capacity in in vitro models to predict the physiological situation. Quercetin showed antioxidant effects in all models and conditions. Prooxidant effect of ‘genistein–daidzein mixture’, at their concentrations reflecting the real life, was suppressed by addition of quercetin to the mixture. Our study shows that flavonoids can exert prooxidant effects depending on the conditions, but the mixture effect should be considered while assessing their effects and safety in humans.