摘要：The main objective of this investigation is to study the influence of arc constriction current frequency(ACCF)on tensile properties and microstructural evolution of aerospace Alloy 718 sheets(2 mm in thickness)joined by constricted arc TIG(CA-TIG)welding *** variable at a time approach of design of experiments(DOE)was used,in which ACCF was varied from 4 to 20 kHz at an interval of 5 levels while other parameters were kept *** joints welded using ACCF of 4 kHz exhibited superior tensile properties extending joint efficiency up to 99.20%.It is attributed to the grain refinement in fusion zone leading to the evolution of finer,discrete Laves phase in interdendritic *** increase of ACCF above 12 kHz caused severe grain growth and evolution of coarser Laves phase in fusion *** 718 welds showed more obvious tendency for Nb segregation and Laves phase formation at higher levels of ACCF due to the slower cooling *** volume fraction of Laves phase was increased by 62.31%at ACCF of 20 kHz compared to that at 4 kHz,thereby reducing the tensile properties of *** is mainly due to the stacking of heat input in weld thermal cycles at increased levels of ACCF.

摘要：为准确获得特高压直流输电系统阀厅内部典型空气间隙放电特性,以进一步指导阀厅设计和优化,针对阀厅内部典型空气间隙开展操作冲击放电试验,采用升降法获得不同空气间隙距离d对应的50%操作冲击放电电压U50,并拟合出相应的U50与d的幂指数曲线,分析了阀厅内部典型空气间隙操作冲击放电特性。同时,在试验过程中改变了均压球的直径并增加了模拟墙,完成了其对放电电压影响的对比试验。结果表明:操作冲击电压随空气间隙距离的增大而不断增加,增大电极曲率半径可以显著提高耐受操作冲击的能力;由不同电极构成的空气间隙耐受操作冲击的能力差异主要体现为放电特性曲线的增加率不同;对于同一种空气间隙,正向操作冲击电压施加在不同电极上会造成放电特性不同;对于更高电压等级的特高压直流输电工程,可以使用更大曲率半径的电极来提高其耐受操作冲击的能力。

摘要：Rapid industrialization has accordingly increased the demand for *** has resulted in the increasingly severe energy and environmental *** production,based on the photocatalytic water splitting driven by sunlight,is able to directly convert solar energy into a usable or storable energy resource,which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental ***,the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical *** construction of heterostructured photocatalyst systems,which are comprised of multiple components or multiple phases,is an efficient method to facilitate the separation of electron‐hole pairs to minimize the energy‐waste,provide more electrons,enhance their redox ability,and hence improve the photocatalytic *** summarize the recent progress in the rational design and fabrication of nanoheterostructured *** heterojunction photocatalytic hydrogen generation systems can be divided into type‐I,type‐II,pn‐junction and Z‐scheme junction,according to the differences in the transfer of the photogenerated electrons and ***,a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.

摘要：甲烷无氧偶联是一种很有前景的甲烷转化利用的增值途径.由于高温条件下催化剂表面反应与气相自由基反应共存且均对产物分布具有重要影响,因而很难深入理解该反应的机理.本文采用火焰喷雾热解方法制备了一系列具有高度分散Mo位点的Mo掺杂的CeO_(2)样品,并用于催化甲烷无氧偶联反应.结果表明,在气相产物中,附加值较高的C2烃产物(乙烷和乙烯)的选择性可达98%.反应过程中催化剂中高度分散的Mo-oxo物种被还原并转化为Mo(oxy-)碳化物物种,它是甲烷活化的活性位点.通过改变反应器内气相部分(即无催化剂部分)的体积,研究了气相反应对于产物分布的贡献.乙烷是甲烷无氧偶联的初级产物,部分乙烯和大部分苯是通过气相化学形成的.综上,本文为甲烷无氧偶联高效催化剂的设计提供了参考,并明确了减少反应器中自由体积以限制二次气相反应的重要性.

摘要：Photocatalytic H2 evolution reactions on pristine graphitic carbon nitrides(g-C3N4),as a promising approach for converting solar energy to fuel,are attractive for tackling global energy concerns but still suffer from low *** this article,we report a tractable approach to modifying g-C3N4 with vanadyl phthalocyanine(VOPc/CN)for efficient visible-light-driven hydrogen production.A non-covalent VOPc/CN hybrid photocatalyst formed viaπ-πstacking interactions between the two components,as confirmed by analysis of UV-vis absorption *** VOPc/CN hybrid photocatalyst shows excellent visible-light-driven photocatalytic performance and good *** optimal conditions,the corresponding H2 evolution rate is nearly 6 times higher than that of pure *** role of VOPc in promoting hydrogen evolution activity was to extend the visible light absorption range and prevent the recombination of photoexcited electron-hole pairs *** is expected that this facile modification method could be a new inspiration for the rational design and exploration of g-C3N4-based hybrid systems with strong light absorption and high-efficiency carrier separation.

摘要：研学旅行是教育和旅游相融合的产物,作为一门课程,将被纳入中国中小学课程体系中。近两年全国各地越来越多的学校和校外研学机构开始尝试因地制宜地设计研学旅行课程,并组织学生开展相关的实践活动,然而该领域的课程建设仍处于起步的摸索阶段,实践者大多根据自己的理解和偏好进行课程设计,缺乏统一的标准指导课程研发。鉴于此,拟在调研国外研学旅行发展经验以及国内已有研学旅行课程研究的基础上,尝试提出核心素养融入的中国研学旅行课程标准,内容包括研学旅行课程的定位、原则、目标设计、内容框架、活动建议、课程设计与实施建议等,以期为我国接下来大规模的中小学生研学旅行课程建设与应用提供借鉴。

摘要：提出了一种高精度、大行程的原子力显微镜探针结构,可用于测量大面积的微观结构表面.该探针结构包括一个硅悬臂梁和一个环形的预压型压电(PZT)执行器,执行器沿Z轴的行程为70μm,其内部集成了一个具有纳米级分辨率的小型线性编码器,可用于测量PZT执行器的位移.编码器的刻度沿执行器的轴向(Z轴)排列以消除阿贝误差.此线性编码器使原子力显微镜探针PZT执行器的行程范围内具有1nm的分辨率,原子力显微镜探针结构联接有两个线性平移台,可用于X和Y方向扫描样本,扫描面积为50mm(X)×40mm(Y).X向平移台和Y向平移台的移动量可由线性编码器测得,分辨率为纳米级.进行了正弦曲面的测量实验.

摘要：本研究通过省、县、乡关键人物的小组讨论和评估,设计出能够解决四川藏族牧民季节性缺乏现金的困难,从而提高牧民基本卫生服务可及性的筹资方案。通过县乡讨论和研讨会设计了6个以借、贷为核心的方案,然后在省级研讨会上,以运作的制度环境以及自然环境评价为基础,依据6项评价指标,最终设计、筛选出一个“小额卫生信贷”方案。可持续性分析表明,对乡卫生院而言,选中的方案具有盈利的可能。

摘要：Solid-state ultraviolet(UV)lasers are widely used for their various applications in commercial and scientific *** nonlinear optical(NLO)crystals with high NLO coefficients and good quality are key factors for the harmonic generation of UV light sources[1-3].The fourth harmonic generation(FHG)using NLO crystals is an effective method to achieve a high-power UV laser at 266 nm[4,5].

摘要：电磁环境是制约电网建设和发展的一个重要因素。研究输电线路电磁环境影响因素及其防护对策,可以为输电线路的设计提供技术依据,使人们正确认识输电线路电磁环境并合理选择防护对策。为此,笔者基于等效电荷法,研究了输电线路对地高度、双回路导线相序布置、等效半径、单回路导线布置方式、相间距离等因素对500kV超高压输电电磁环境的影响,并根据研究结论和相关研究成果提出了主动防护和被动防护等具体的防护对策。