Theoretical Investigation on Photoionization and Dissociative Photoionization of Toluene

The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods.The geometries and frequencies of the reactants,transition states and products have been performed at B3LYP/6-311++G (d,p) level,and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level.The ionization energies of toluene and the appearance energies for major fragment ions,C₇H₇⁺,C₆H₅⁺,C₅H₆⁺,C₅H₅⁺,are determined to be 8.90,11.15 or 11.03,12.72,13.69,16.28 eV,respectively,which are all in good agreement with published experimental data.With the help of available published experimental data and theoretical results,four dissociative photoionization channels have been proposed:C₇H₇⁺+H,C₆H₅⁺+CH₃,C₅H₆⁺+C₂H₂,C₅H₅⁺+C₂H₂+H.Transition structures and intermediates for those isomerization processes are determined in this work.Especially,the structures of C₅H₆⁺ and C₅H₅⁺ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.     

Coupling Reactions of Alkynyl Indoles and CO2 by Bicyclic Guanidine: Origin of Catalytic Activity?

Density functional theory calculations were used to investigate the three possible modes of activation for the coupling of CO₂ with alkynyl indoles in the presence of a guanidine base. The first of these mechanisms, involving electrophilic activation, was originally proposed by Skrydstrup et al. (Angew. Chem. Int. Ed . 2015 , 54 , 6682). The second mechanism involves the nucleophilic activation of CO₂. Both of these electrophilic and nucleophilic activation processes involve the formation of a guanidine‐CO₂ zwitterion adduct. We have proposed a third mechanism involving the bifunctional activation of the bicyclic guanidine catalyst, allowing for the simultaneous activation of the indole and CO₂ by the catalyst. We demonstrated that a second molecule of catalyst is required to facilitate the final cyclization step. Based on the calculated turnover frequencies, our newly proposed bifunctional activation mechanism is the most plausible pathway for this reaction under these experimental conditions. Furthermore, we have shown that this bifunctional mode of activation is consistent with the experimental results. Thus, this guanidine‐catalyzed reaction favors a specific‐base catalyzed mechanism rather than the CO₂ activation mechanism. We therefore believe that this bifunctional mechanism for the activation of bicyclic guanidine is typical of most CO₂ coupling reactions.     

Nanostructured heterogeneous catalysts for electrochemical reduction of CO2

Electrochemical reduction of CO₂ provides a sustainable solution to address the intermittent renewable electricity storage while recycling CO₂ to produce fuels and chemicals. Highly efficient catalytic materials and reaction systems are required to drive this process economically. This Review highlights the new trends in advancing the electrochemical reduction of CO₂ by developing and designing nanostructured heterogeneous catalysts. The activity, selectivity and reaction mechanism are significantly affected by the nano effects in nanostructured heterogeneous catalysts. In the future, energy efficiency and current density in electrochemical reduction of CO₂ need to be further improved to meet the requirements for practical applications.     

Advanced response surface method for mechanical reliability analysis

Based on the classical response surface method (RSM), a novel RSM using improved experimental points (EPs) is presented for reliability analysis. Two novel points are included in the presented method. One is the use of linear interpolation, from which the total EPs for determining the RS are selected to be closer to the actual failure surface; the other is the application of sequential linear interpolation to control the distance between the surrounding EPs and the center EP, by which the presented method can ensure that the RS fits the actual failure surface in the region of maximum likelihood as the center EPs converge to the actual most probable point (MPP). Since the fitting precision of the RS to the actual failure surface in the vicinity of the MPP, which has significant contribution to the probability of the failure surface being exceeded, is increased by the presented method, the precision of the failure probability calculated by RS is increased as well. Numerical examples illustrate the accuracy and efficiency of the presented method.     

三峡库区万州段高切坡破坏模式和防护措施研究

高切坡是三峡库区新的地质灾害形式。通过对重庆库区万州区47个高切坡的调查和试验分析表明,万州高切坡主要表现为崩塌破坏、表层风化破坏、差异风化破坏、和土体滑塌破坏4种形式。影响破坏模式的因素主要是构成高切坡的组成物质及其性质、水文气象条件、高切坡的形态和治理时间等。针对不同的破坏类型提出相应的防治措施,以指导设计与施工。     

基于SMP破坏准则的饱和砂土弹塑性本构模型

利用土体的塑性流动理论，提出了用于描述饱和砂土在单调荷载作用下的应力一应变反应性质的弹塑性本构模型。土体总的变形由三部分组成：即弹性应变、与体积屈服机制相关的塑性应变和与剪切屈服机制相关的塑性应变，其中与剪切屈服机制相关的塑性应变的得出是基于SMP破坏准则。通过将模型预测的结果与试验结果进行对比，表明该模型能够较为准确地描述饱和砂土在单调加载条件下的反应性质。     

Three-Dimensional Dynamic Contact Problem for an Elliptic Crack Interacting with a Normally Incident Harmonic Compression–Expansion Wave

The paper deals with the three-dimensional dynamic problem for an elliptic crack interacting with a normally incident harmonic compression–expansion wave, considering the contact interaction of the crack faces. An asymmetric solution is obtained using an iteration algorithm developed earlier. Numerical results are presented     

多胞材料的力学行为

多胞材料具有独特的力学性质,其工程应用日益增加.人造多胞材料可以分为蜂窝材料和泡沫材料两类.本文介绍了这两类材料在不同载荷条件下力学行为的研究概况.对于某些天然材料(木材和松质骨)的多胞结构及其模型也作了简要介绍.     

伪可变体系的几何构造分析

伪可变体系几何可变性的研究，对轻型结构的设计分析已变得十分重要。本文先分析能量与平衡之间的普遍关系，进而得出判定体系可变性的能量准则。通过拉格朗日乘子的引入，建立能量泛函，得出判定极值的二次型。然后证明了乘积力法与能量法的一致性，并讨论了宜于计算机分析实现的矩阵表示方法。结果表明，若二次型确定，则体系伪可变；当半确定时，体系部分伪可变部分可变；否则体系含二阶以上的无穷小机构。     

聚晶立方氮化硼刀具切削高锰钢的磨损机制

在半精加工试验条件(切削深度ap=0．5mm，进给量f=0．3mm／r，干切)下研究了聚晶立方氮化硼刀具切削奥氏体高锰钢时的磨损机制，用WDH-Ⅱ型光电温度计测量了切削温度，用工具显微镜测量后刀面磨损量，进而考察了切削时间和切削速度对后刀面磨损量的影响，采用S-250MK型扫描电子显微镜观察刀具前、后刀面的磨损形貌和组成变化．结果表明：当切削温度为400～750℃时，聚晶立方氮化硼刀具同高锰钢中的γ相及其析出相(Fe，Mn)3C之间产生严重的机械磨损；当切削温度超过800℃时，聚晶立方氮化硼刀具同高锰钢单一γ相之间产生扩散磨损；聚晶立方氮化硼刀具适合于高速切削.