Theoretical research on the H2 generation mechanism on Pt6, Pt5Sn5 and Pt3Sn6 clusters by density functional theory

In this paper, the mechanisms of H₂ evolution on Pt₆, Pt₅Sn₅, and Pt₃Sn₆ clusters were respectively investigated by the B3LYP method of density functional theory (DFT). The B3LYP functional with non-local dispersion corrections (B3LYP-D3) method were performed to investigate the adsorption of H and H⁺ on clusters. The calculation results indicated that the adsorption energy of H on Pt reduced due to the interaction of Sn and Pt, which promoted H desorption from Pt to form H₂. Meanwhile, Sn atom of Pt₅Sn₅ and Pt₃Sn₆ clusters had strong interaction with H⁺ due to the existence of Pt, which was benefit for the reduction of H⁺ on Sn atom. As a consequence, Pt₅Sn₅ and Pt₃Sn₆ showed lower potential barrier and higher activities than Pt for H₂ evolution. The potential barriers of H₂ formation over Pt₃Sn₆ clusters was only 11.1% of that over Pt cluster.     

Kinetic parameters of anodic oxidation of methanol in alkali: Effect of diameter of Pd nano-catalyst,composition of electrode and solution and mechanism of the reaction

Palladium nanoparticles with varying particle diameter (6.9–25.1 nm) have been synthesized by single-pot wet chemical technique in presence of poly vinyl alcohol by controlling the duration of reflux. The resulting nanoparticles have been dip-coated on Ni-foil, followed by determination of kinetic parameters of the anode-catalysts in reference to alkaline oxidation of methanol (AOM) by electrochemical and IR-spectroscopic techniques. The morphology and surface characteristics of the Pd nano-catalyst have been investigated by electron microscopy in conjugation with energy dispersion spectroscopy. The results show the formation of formate and carbonate with no change in selectivity but improved kinetic parameters on decreasing the diameter of constituting Pd nanoparticles. The studies of cyclic voltammetry of methanol, formaldehyde and formate reveal that the electrode constituted with Pd nanoparticles having average diameter of 6.9 nm obtained by applying the lowest time (0.33 h) of reflux, is the best for all the fuels. The studies also help understanding the stability of the electrodes, proposition of the intermediates and plausible mechanism of the reaction.     

Internal abstraction of dynemicin A: An MD approach

Dynemicin A has the ability to undergo the Bergman cyclization, forming a para-benzyne moiety with the ability to induce DNA strand scission. This property of dynemicin A makes it a promising anti-tumor agent. Past research has shown conclusively that dynemicin A binds to and abstracts a hydrogen atom (H5′) from the DNA backbone, but the molecular mechanism of the binding event is not fully understood. We have used AMBER Molecular Dynamics simulations to investigate the dynamics associated with the reaction mechanisms. Previously, two binding mechanisms have been proposed, of which the second is more supported: (1) dynemicin A intercalates between two base pairs and directly abstracts a hydrogen atom from DNA and (2) dynemicin A inserts into the minor groove and directly abstracts a hydrogen atom from DNA. We propose a third mechanism, where dynemicin A intercalates, then undergoes a proximate, intramolecular hydrogen atom abstraction (internal abstraction). While not studied here, the resulting radical would then subsequently abstract a hydrogen atom from DNA.     

One-step versus two-step mechanism of Diels-Alder reaction of 1-chloro-1-nitroethene with cyclopentadiene and furan

DFT computational study shows that Diels-Alder (DA) reactions of 1-chloro-1-nitroethene with cyclopentadiene and furan have polar nature. However, their mechanism is substantially different. In particular, 1-chloro-1-nitroethene react with cyclopentadiene according to one-step mechanism. In the same time, more favourable channel associated with the P-DA reaction between furan and 1-chloro-1-nitroethene is a domino process, that comprises an initial hetero-Diels-Alder reaction yielding a [2 + 4] cycloadduct, which experiences a subsequent [3,3] sigmatropic shift to yield the expected formal [4 + 2] cycloadduct. This is a consequence of more polar nature of reaction, due to higher nucleophilicity of furan in comparison to cyclopentadiene.     

How does aluminium foaming agent impact the geopolymer formation mechanism?

Aluminium is widely used as a foaming agent in lightweight geopolymer concretes. The impact of aluminium reaction on the phase evolution of fly-ash based geopolymers is investigated. In-situ Fourier transform infrared spectroscopy (FTIR) is used to track the changes in the nanostructure of geopolymers. By combining the FTIR functional group analysis with Atomic-force microscopy (AFM) results, it is possible to evaluate the phase development during the early hours of reaction. At the initial stages of geopolymerization, aluminium reaction induces the formation of aluminium hydroxide gel which precipitates on fly ash and conceals the reactive surface of ash particles. Therefore, the dissolution rate of fly ash declines and the strength development is delayed. The high release rate of alumina into the solution, as a result of the aluminium metal reaction, leads to a better connectivity of unreacted particles and better microstructural development as shown in SEM images. Also, by consuming part of the sodium hydroxide catalyst at the beginning of the reaction, aluminium powder protects some of the alkali content of geopolymer matrix from carbonation.     

渤南低渗油田注水井欠注层伤害机理研究

渤南油田五区沙三段九砂组油藏属中等水敏性和速敏性的地层;油藏为轻质油-稀油油藏。原油具有低密度、低粘度和高凝固点等特点,组分含硫量低;地层水总矿化度较高,水型为NaHCO3型。研究了渤南油田注水井伤害机理,从地层特性、注入水水质、悬浮物堵塞、游离油和乳化油滴、结垢、细菌及以往增产措施等方面评价了可能对储层造成的损坏及损坏程度。渤南油田地层的水敏性、速敏性和低渗透性是注水井损害的内在因素,注水井中悬浮固相颗粒、含油量和细菌严重超标,水质不合格是注水井损害的外在因素;注入水中悬浮固相颗粒和油的含量高,易形成盐酸不溶垢和有机垢;细菌和油质的共同作用增加管路的腐蚀,形成铁垢,逐渐降低地层的渗透率,严重时堵塞地层。     

玻璃相与陶瓷金属化技术

本文叙述了陶瓷金属化技术的发展过程和玻璃相在金属化技术中的重要作用.讨论了几种主要金属化机理,提出了陶瓷中玻璃相和金属化层中玻璃相的相互关系.     

一种基于监控视频的出租车识别方法

研究了一种基于视频监控的出租车识别算法.对已经完成跟踪的车辆,通过提取车辆的方向梯度直方图(HOG)特征,作为支持向量机(SVM)分类检测的输入,进行车辆是否为出租车的分类识别.通过多窗口投票机制,增强了分类识别算法的准确性与鲁棒性.实验证明,该方法能准确进行出租车的分类识别,基于实际的标清监控视频,出租车的分类准确率达到90％左右.     

基于秀丽隐杆线虫模型探讨白芥子水提物抗氧化作用及机制

摘 要：目的 研究白芥子水提物抗氧化活性,探讨其抗氧化的相关机制。方法 采用2,2-联苯基-1-苦基肼基(2,2-Diphenyl-1-picrylhydrazyl,DPPH)自由基、羟基自由基、铁离子还原能力3种方法对其体外抗氧化活性进行评价。采用秀丽隐杆线虫野生型N2线虫观察白芥子水提物对线虫寿命、运动能力、生殖能力的影响;通过氧化应激、热应激、脂褐素和活性氧(reactive oxygen species, ROS)评估其对线虫抗氧化能力的影响。采用实时荧光定量技术测定白芥子水提物作用下线虫抗氧化、胰岛素信号途径相关基因表达情况。结果 白芥子水提物具有一定的DPPH·、羟基自由基清除能力。通过氧化应激筛选出最佳给药浓度为10 mg/mL,且该给药浓度对线虫的运动能力和生殖能力无影响(P>0.05),并能够显著延长线虫的平均寿命和中位寿命(P<0.01);10 mg/mL给药组显著提高线虫抗热应激能力,降低脂褐素积累和ROS水平;同时上调daf-16、sod-3、clt-2、skn-1的mRNA表达量,下调daf-2的mRNA的表达量。结论 白芥子具有良好的体内外抗氧化能力,可能与调控胰岛素/胰岛素样生长因子(insulin like growth factor, IGF)-1信号(insulin/IGF-1 signaling, IIS)通路上的基因表达有关。     

化学镀非晶Ni-P/Ni-Mo-P合金形成机理

通过在镀液中加入Na2 MO4的化学沉积法对酸性Ni Mo P/Ni P双层化学镀的工艺进行了实验研究。通过一系列实验 ,确定了用连续施镀法制备此多元合金镀层的工艺。通过对镀层的成分与结构关系及镀层成分与工艺参数关系的实验研究 ,从热力学角度提出了非晶态双层镀镀层合金膜材的形成机理。