Surfactant‐Free Sub‐2 nm Ultrathin Triangular Gold Nanoframes

Ultrathin triangular gold nanoframes are synthesized in high yield through selective gold deposition on the edges of triangular silver nanoprisms and subsequent silver etching with mild wet etchants. These ultrathin gold nanoframes are surfactant‐free with tailorable ridge thickness from 1.8 to 6 nm and exhibit adjustable and distinct surface plasmon resonance bands in the visible and near‐IR region. In comparison, etching of the nanoprism template by galvanic replacement can only create frame structures with much thicker ridges, which have much lower catalytic activity for 4‐nitrophenol reduction than the ultrathin gold nanoframes.     

Global and Local Mechanical Properties of Autogenously Laser Welded Ti-6Al-4V

Ti-6Al-4V sheets, 3.2-mm in thickness, were butt welded using a continuous wave 4 kW Nd:YAG laser welding system. The effect of two main process parameters, laser power and welding speed, on the joint integrity was characterized in terms of the joint geometry, defects, microstructure, hardness, and tensile properties. In particular, a digital image correlation technique was used to determine the local tensile properties of the welds. It was determined that a wide range of heat inputs can be used to fully penetrate the Ti-6Al-4V butt joints during laser welding. At high laser power levels, however, significant defects such as underfill and porosity, can occur and cause marked degradation in the joint integrity and performance. At low welding speeds, however, significant porosity occurs due to its growth and the potential collapse of instable keyholes. Intermediate to relatively high levels of heat input allow maximization of the joint integrity and performance by limiting the underfill and porosity defects. In considering the effect of the two main defects on the joint integrity, the underfill defect was found to be more damaging to the mechanical performance of the weldment than the porosity. Specifically, it was determined that the maximum tolerable underfill depth for Ti-6Al-4V is approximately 6 pct of the workpiece thickness, which is slightly stricter than the value of 7 pct specified in AWS D17.1 for fusion welding in aerospace applications. Hence, employing optimized laser process parameters allows the underfill depth to be maintained within the tolerable limit (6 pct), which in turn prevents degradation in both the weld strength and ductility. To this end, the ability to maintain weld ductility in Ti-6Al-4V by means of applying a high energy density laser welding process presents a significant advantage over conventional arc welding for the assembly of aerospace components.     

超高层建筑配变电所及其设备运输通道

超高层建筑配变电所的设置不仅要考虑合适的位置、合理的数量,而且要考虑设备的运输通道,满足将来设备更替的需求.     

Stochastic learning and optimization — Ideas vs mathematics?

What are the roles that ideas and mathematics play in research of engineering subjects? This article tries to answer this question with the author’s own research experience. In the past 30 years, the author’s research started from perturbation analysis (PA) of queueing networks, to PA of Markov systems, to Markov decision processes (MDP), and to stochastic control; and based on these research, the author has successfully developed a sensitivity-based optimization approach to the area of learning and optimization of stochastic systems, leading to a simple and unified framework for the area, new research directions, and new results in the area. This paper reviews the above research topics and the history of their development with an emphasis on what the roles that ideas and mathematics play in each of the advances along the path.     

Stress induced crystallization of hydrogenated amorphous silicon

Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiN_x and Al₂O₃ capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry.     

Surface chemistry features in the flotation of KCl

Despite the successful industrial practice to recover KCl by flotation, the adsorption state of collectors at KCl salt surfaces is still not fully understood. In this paper, the flotation behavior of KCl and NaCl using different collectors and captive bubble contact angle measurements at KCl and NaCl crystal surfaces in their saturated solutions are reported. The influence of collector concentration and collector structure is considered. The results show that both cationic and anionic collectors produce a hydrophobic state at the structure breaking KCl salt surface, with finite contact angle values of between 30° and 60°. In contrast, the contact angle at the structure making NaCl salt surface is zero at all collector concentrations, suggesting that no collector adsorption occurs, a supposition that is supported by results from molecular dynamics simulation (MDS). Further, it appears that the presence of surface defects such as edges and corners promote the adsorption of collectors at the KCl surface, and that the flotation is achieved by bubble attachment at the edges/corners of KCl particles with the formation of aeroflocs.     

An AM-RLC scheme with adaptive acknowledgement interval

The acknowledged mode radio link control (AM-RLC) protocol is one of the most important radio protocols in wideband code division multiple access (WCDMA) and time division-synchronization code division multiple access (TD-SCDMA) mobile communication systems. A modified AM-RLC scheme with adaptive acknowledgement interval is proposed. At the receiver, the acknowledgement interval is dynamically changed according to the channel status. The simulation results show that the proposed AM-RLC scheme outperforms the fixed acknowledgement interval AM-RLC scheme in terms of frame delivery delay and protocol overhead. __________ Translated from Journal on Communications, 2008, 29(3): 119–122 [译自: 通信学报]     

基于MCGS的退火窑集散式测试系统研究

以基于MCGS的退火窑集散式测试系统的搭建过程为例，详细的论述了MCGS工程组态软件工程组态的过程。最终实验结果表明了该方案的有效性和正确性，并具有实际的应用价值。     

Effects of laser shock processing,solid solution and aging,and cryogenic treatments on microstructure and thermal fatigue performance of ZCuAl10Fe3Mn2 alloy

The materials used in variable temperature conditions are required to have excellent thermal fatigue performance. The effects of laser shock processing (LSP), solid solution and aging treatment (T6), and cryogenic treatment (CT) on both microstructure and thermal fatigue performance of ZCuAl₁₀Fe₃Mn₂ alloys were studied. Microstructure and crack morphology were then examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The result showed that, after being subjected to the combination treatment of T6+CT+LSP, the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl₁₀Fe₃Mn₂ alloy with the tensile strength, hardness, and elongation of 720 MPa, 300.16 HB, and 16%, respectively, and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm. Moreover, the ZCuAl₁₀Fe₃Mn₂ after combination treatment shows high resistance to oxidation, good adhesion between the matrix and grain boundaries, and dramatically reduced growth rate of crack. During thermal fatigue testing, under the combined action of thermal and alternating stresses, the microstructure around the sample notch oxidized and became loose and porous, which then converted to micro-cracks. Fatigue crack expanded along the grain boundary in the early stage. In the later stage, under the cyclic stress accumulation, the oxidized microstructure separated from the matrix, and the fatigue crack expanded in both intergranular and transgranular ways. The main crack was thick, and the path was meandering.     

铝合金无沉淀析出带的研究进展

综述了过去50年来铝合金中无沉淀析出带(PFZ)的研究,重点论述了PFZ的主要形成机理、影响因素及其对合金性能(主要为力学性能和耐腐蚀性能)的影响,系统介绍了PFZ在形成机理及对合金性能上所持的不同观点及其相关理论。最后,提出了对铝合金中PFZ方面存在的难点以及重点研究方向。