Reinforcing effect of laminate structure on the fracture toughness of Al3Ti intermetallic

Metal/intermetallic laminate composites can improve the mechanical properties of intermetallic materials using metal layers. In recent years, titanium aluminide intermetallics have received increasing attention due to their excellent performance properties, such as high melting point, high specific strength and stiffness, and good corrosion resistance. However, the low fracture toughness of Al3Ti alloys at room temperature has greatly limited their application, and fiber or particle reinforcement has not shown a significant toughening effect. Research into the reinforcing effects of the interface and near-interface zone on the fracture behavior of Al3Ti is lacking. Ti/Al3Ti metal/intermetallic laminate composite was synthesized from titanium and aluminum foils using vacuum hot-pressed sintering technology. The microstructure of the prepared material was analyzed by scanning electron microscope and electron backscattered diffraction. Results illustrate that both Ti and Al3Ti were single-phase and there was a noticeable stress concentration on the interface. To obtain indentation and cracks, loads were applied to different locations of the composite by a microhardness tester. The growth path of the cracks was then observed under microscope, showing that crack propagation was prevented by the interface between the Ti and Al3Ti layers, and the cracks that propagated parallel to the laminate shifted to the interface. Fracture toughness of the different areas, including Al3Ti layers, interface, and near-interface zone, were measured by the indentation fracture method. The fracture toughness at and near the interface was 1.7 and 2 times that of the Al3Ti layers, respectively. Results indicate that crack blunting and crack front convolution by the laminate structure was primarily responsible for increased toughness.     

幂函数不均匀生长率对KPZ方程标度行为的影响

通过对含有不均匀生长项的KPZ主程进行动力学重整化群分析,研究了幂函数不均匀生长KPZ方程标度行为的影响,在实际的晶体生长过程中,生长率的不均一可以由表面杂质和缺陷引起,研究表明,生长率不均匀性的存在,能显著地改变KPZ方程的标度性质,粗糙度指数Z和动力学指数都与基底的维数d和幂指数（ε＋1）有关。     

关于建立地理科学体系的几点认识

地理科学是自然科学与社会科学的交叉。近代地理学的发展,在协调人类活动和自然环境的相互关系和相互作用方面做出积极贡献。地理科学是开放的、复杂的巨系统,要广泛应用新技术新手段,提高地理科学的研究水平。还要吸收其他学科有用的理论和方法。加强理论研究和生产实践相结合,地理科学才能取得不断发展。     

Microstructure evolution and nucleation mechanism of Inconel 601H alloy welds by vibration-assisted GTAW

Nickel-based alloys exhibit excellent high-temperature strength and oxidation resistance; however, because of coarse grains and severe segregation in their welding joints, these alloys exhibit increased susceptibility to hot cracking. In this paper, to improve the hot-cracking resistance and mechanical properties of nickel-based alloy welded joints, sodium thiosulfate was used to simulate crystallization, enabling the nucleation mechanism under mechanical vibration to be investigated. On the basis of the results, the grain refinement mechanism during the gas tungsten arc welding (GTAW) of Inconel 601H alloy under various vibration modes and parameters was investigated. Compared with the GTAW process, the low-frequency mechanical vibration processes resulted in substantial grain refinement effects in the welds; thus, a higher hardness distribution was also achieved under the vibration conditions. In addition, the γ' phase exhibited a dispersed distribution and segregation was improved in the welded joints with vibration assistance. The results demonstrated that the generation of free crystals caused by vibration in the nucleation stage was the main mechanism of grain refinement. Also, fine equiaxed grains and a dispersed γ' phase were found to improve the grain-boundary strength and reduce the segregation, contributing to preventing the initiation of welding hot cracking in nickel-based alloys.     

交际策略与外语输出能力

旨在阐明交际策略与外语输出能力之间存在的关系。作者对在外语教学中如何进行交际策略的培养，来提高外语学习者的外语输出能力方面的问题提出了相关的见解与看法。     

具有多级缓冲的快速光子计数器

数字光子相关仪主要由光电计数电路和数椐处理电路组成。光电计数电路作为系统的数据采集部分其性能直接影响处理结果,采用带有多级缓冲区的快速进位光子计数器,可准确动态地采集光电子脉冲数并由单片机进行处理。     

DNS of the turbulence modulation by dispersed particles in compressible spatially developing two-phase jets

A new two-way coupled direct numerical simulation (DNS) method is developed to study the turbulence modulation in the compressible and spatial developing particle-laden turbulent jets with higher Reynolds number. The high-resolution solver is performed for the gas phase flow-field and the Lagrangian method is used to trace particles. It is found that the particles with Stokes number of 0.01and 50 advance the evolution of the coherent structures in the flow-field, but the particles with Stokes number of 1 delay it. All particles increase the turbulent kinetic energy and decrease the vorticity thickness, in which the particles with the Stokes number of 1 exhibit the maximum modulation. The jet velocity half-width and the decay of the streamwise mean velocity along the centerline are reduced by particles with Stokes number of 0.01 and 1. The momentum thickness is increased by particles and the larger the Stokes number is, the larger the momentum thickness is.     

Expression of reconstructive hFⅧ in the hrDNA by using hrDNA targeting vector

Our lab has constructed a new nonviral vector-hrDNA targeting vector（pHrneo）, pHrneo is a human derived vector that can target gene into human ribosomal DNA（hrDNA） locus. In this study, we inserted expression cassette of reconstructive hF Ⅷ （hFⅧ-BDDAK39） to pHrneo to construct targeting vector： pHrneo-BDDAK39. Through electroporation of pHrneo-BDDAK39 into HT1080 cells, we identified the homologous recombinants by PCR and Southen blotting, and tested the expression of hFⅧ- BDDAK39 in the hrDNA locus. The hFⅧ-BDDAK39 was successfully targeted into hrDNA locus of HT-1080 by pHrneo-BDDAK39, and the efficiency of site-specific integration was 2.0×10^-5. hFⅧ-BDDAK39 in hrDNA locus of HT-1080 is found to be able to express efficiently （32±5 ng·10^6 cells^-1 .24 h^-1）. Targeting vector pHrneo-BDDAK39 can find use in gene therapy for hemophilia.     

Nb离子注入Ti—Al合金的氧化性能研究

研究了不同注量Nb离子注入的Ti－Al合金（Al的原子分数为48％）在900,950℃静止空气中的恒温氧化行为．研究发现：注量为3×1017cm(-2)的Nb可以显著改善该合金的高温抗氧化能力;随注量的增加（3×1015→3×10(17)cm(-2)）,其改善能力得到增强;离子注入Nb是通过改变氧化反应初期的氧化形式和Ti－Al合金氧化层的显微结构而发挥作用的．