高铁开通与股价崩盘风险

近年来,中国高速铁路迅猛发展。本文利用高铁开通这一自然实验衡量经济主体间信息不对称和监管成本的降低,采用双重差分法,从股价崩盘风险的角度研究了高铁开通对资本市场的影响及其经济后果。文章研究发现高铁的开通带来了所在地上市公司股价崩盘风险的降低,这一关系在只开通非城际高铁和同时开通城际和非城际高铁的年度更为显著。进一步渠道分析发现,高铁开通对股价崩盘风险的降低作用在信息不对称程度较高和外部监管环境较弱的情况下更为显著。文章结果表明高铁的开通促进了信息的跨地区流动,有利于上市公司治理环境的提高,提供了我国基础设施建设对资本市场环境影响的经验证据。国家自然科学基金重大项目课题“制度变革、非正式制度因素与会计审计行为”(71790602);国家自然科学基金项目“事务所规模与审计质量:团队视角”(71672159);国家自然科学基金重点项目“基于中国情境的企业内部控制有效性研究”(71332004)的资助;;教育部重点研究基地重大项目“资本结构选择与公司治理机制优化”(16JJD790034

Effects of Nd element addition on microstructure refinement of Ti-6Al-4V-2Cr alloy

采用冷等静压–真空烧结法制备Ti-6Al-4V-2Cr-1Nd合金,然后进行固溶及时效热处理,通过实验与最小错配度理论计算,研究Nd元素对该合金组织细化的影响,并分析细化机理。结果表明,添加1%(质量分数)的稀土元素Nd后,析出相Nd2O3能有效促进晶粒细化。二维错配度的计算结果证明析出相Nd2O3是有效的形核剂,可促进非均匀形核,增加形核率,从而使晶粒细化。通过对合金试样薄区进行高分辨率观察,发现另一种絮状的、非常细小的、弥散分布的Nd2Ti4O11相,由于其界面错配度较低,也可作为非均匀形核的核心,促进形核,起到细化晶粒的作用。Titanium alloy Ti-6Al-4V-2Cr-1Nd is made by the cold isostatic pressing and vacuum sintering, then the solution and aging heat treatment was carried on the prepared of titanium alloy, the effect of Nd elements on the microstructure refinement and the refinement mechanism were researched and analyzed through the experiment and theory calculation of minimum mismatch degree. The results show that the main precipitation phase Nd_2O_3 can effectively promote the grain refinement after adding rare earth element 1% Nd(mass fraction). The two-dimensional mismatch degree calculation results proved that the precipitated phase Nd2O3 is the effective nucleating agents that can promote the heterogeneous nucleation and increase the nucleation rate, thus promote the grain refinement. Through the high resolution observation of thin area in the sample, another precipitated phase Nd2Ti4O11 is found, which is flocculent, dispersed and very small. Because of the low degree of interface mismatch, Nd2Ti4O11 can also be used as the core of heterogeneous nucleation and promote nucleation, which means it can also play a role in grain refinement.河南省重大科技专项(102105000007

Effects of Nd element addition on microstructure and mechanical properties of Ti-6Al-4V-2Cr alloy

本试验采用冷等静压法及粉末冶金法制备钛合金,消除了成分偏析对合金性能的影响。在Ti-6Al-4V-2Cr中加入稀土Nd元素并进行热处理,运用光学; 显微镜、XRD和TEM对其组织和性能进行观察和分析。通过观察发现合金的组织为均匀的alpha +; beta相。运用XRD和TEM观察发现,晶界和晶内均有Nd_2O_3析出物,Nd_2O_3的出现细化了晶粒,提高了形核率,降低了晶粒尺寸。运用精; 密万能试验机进行了力学性能测试,当Nd元素含量为1%时,合金的综合力学性能最好,合金的抗拉强度提高了10.7%,伸长率提高了49.1%。The Ti-6Al-4V-2Cr-xNd alloys were prepared by the cold isostatic; pressing method and powder metallurgy with addition of Nd element,the; effect of composition segregation on properties of the titanium alloy; was eliminated,and microstructure and the properties of the alloy after; heat treatment were studied by means of optical microscope,XRD and TEM.; The results show that the microstructure of the Ti-6Al-4V-2Cr-xNd is; composed of homogeneous alpha + beta phase. Nd_2O_3 precipitates are; observed in the grain boundaries and in the grains by XRD and TEM,and it; can refine the grains,increase the nucleation rate and decrease the; grain size. The optimal mechanical properties of the alloy are obtained; when the Nd content is 1%,and the tensile strength and elongation of the; alloy increase by 10.7% and 49.1%,respectively.军工863项目; 国防973支持项

Electrocatalytic Oxidation of Salicylic Acid at Novel Gold Nanoparticle-modified Glassy Carbon Electrode

借助"种子媒介纳米金属生长法"制备新型的纳米金修饰玻碳电极,应用场发射扫描电镜、紫外-可见光谱分析和电化学方法等,研究该电极的表面形貌及其电化学性能.结果表明,该修饰电极对水杨酸的电化学氧化有明显的电催化作用,电极响应灵敏度是裸玻碳电极表面的1.8倍.其氧化峰电流与水杨酸浓度在5.0×10-7~8.0×10-5mol/L范围内呈良好的线性关系,可用于水中痕量水杨酸的检测.A gold nano-particles modified glassy carbon electrode(GNP/GCE) was prepared by the"seed-mediated gold nano-particles growth method".Field emission scanning electron microscopy,ultraviolet-visible(UV-vis) spectroscopy analysis and electroalaylsis were employed to study the morphology and electrochemical performances.The resulting electrode showed excellent electro-catalytic activity toward the oxidation of salicylic acid and the response sensitivity was 1.8 fold than that obtained on GCE.Good linear relationship was obtained between response current and salicylic acid concentration in the range of 5.0 × 10-7 ~8.0 × 10-5 mol/L,which could be used in the detection of trace salicylic acid.作者联系地址：中国地质大学环境学院;华中科技大学环境科学与工程学院;福建师范大学闽南科技学院生化工程系;华中科技大学化学与化工系;Author's Address: 1.School of Environment Studies,China University of Geosciences,Wuhan 430074,China;2.College of Environmental Science and Engineering,Huazhong University of Scienceand Technology,Wuhan 430074,China;3.College of Biochemical Engineering MinnanScience and Technology Institute of Fujian Normal University,Quanzhou 362332,Fujian,China;4.College of Chemistry and Chemical Engineering,Huazhong University of Science and Techonlogy,Wuhan 430074,Chin

Study of the Simulation of Marine Atmospheric Exposure with Lab Accelerated Test of Marine Coating Systems

通过两年海洋大气环境暴露试验、盐雾/紫外冷凝老化交替试验和氙灯老化试验,对比聚氨酯涂料、丙烯酸涂料涂层的色差和失光率,研究了3种试验对涂层表观性能的影响,发现紫外/冷凝老化加速试验对海洋大气暴露试验有很好的模拟性。The simulation of marine atmospheric exposure with lab accelerated test was studied.The lab accelerated test methods were UV-condensation and salt-fog alternant test and Xenon-Arc exposure test.The marine coating systems based on polyurethane and acrylic were compared in color difference and rate of losing gloss.The result showed that UV-condensation and salt-fog alternant test can better simulate the marine atmospheric environment than the Xenon-Arc exposure test

Study on Correlation between Marine Environmental Test and Accelerated Tests in Laboratory for Ship Coatings——Coating Systems for Marine Atmosphere

采用光泽-色泽仪、涂膜粉化率测定仪、fdIr,SEM及AfM等现代测试分析手段,对海洋大气区7种常用舰船涂料体系在实际海洋环境暴露试验以及室内人工加速老化及腐蚀试验前后的涂层性能变化进行了对比分析,并结合厦门地区的气象环境谱探索了实验室加速试验与实际海洋大气暴露试验的相关性。Seven ship coating systems were exposed in marine atmospheric environment and accelerated weathering tests in lab.Some modern analyses,such as gloss and color measurement,coat chalk rating,precise thickness meter,FDIR,SEM,AFM were applied to characterize the properties of the coating systems.The results of performance change before and after exposure were compared.The weather environmental spectrum of Xiamen area was also combined for discussion of the correlation between marine environmental exposure tests and accelerated weathering tests in lab