Gradient microstructure of TC21 alloy induced by hydrogen during hydrogenation

Through melt hydrogenation, a gradient microstructure (α″ + α′)/(α + β_H) has been observed in TC21 alloy. The addition of hydrogen induces martensite transformation and increases the volume fraction of β. It is found that the absorption process of hydrogen atoms can be divided into melting and cooling stages. During cooling, the continuous absorption of hydrogen and the corresponding decrease of freezing point of melt extend solidification time of melt and lead to hydrogen enrichment in the upper of the specimen, which induces the formation of the gradient structure. The hydrogenated TC21 alloy shows higher thermoplasticity compared with the unhydrogenated TC21 alloy. The flow stress of the upper part of the hydrogenated alloy is lower than that of the center part. A gradual variation has been observed in the microhardness along the gradient direction due to variation in the microstructure. The microhardness of the upper surface drops about 45% with 14.6 at.%H.     

Wear mechanisms of micro-drills during dry high speed drilling of PCB

In this paper, micro-drills with diameters of 0.1–0.3 mm were used to drill printed circuit boards (PCBs) with a highest spindle speed of 300 krpm. To study the wear mechanisms of PCB micro-drills, micro-drill morphology was observed, and the flank wear of the micro-drills was measured. The factors affecting flank wear were studied. In addition, hole wall roughness, nail head formation, and the accuracy of hole location were measured and analysed to determine how micro-drill wear influenced hole quality. It was found that abrasion was the main mechanism controlling the deterioration of cemented tungsten carbide micro-drills. The aggressive rubbing by glass fibre broken chips and reinforcing fillers, and the diffusion of cobalt caused abrasive wear of the flank, the chisel edge, the rake face, and the minor flank of the micro-drills. Resin that was softened by cutting heat would adhere to the micro-drills, which decreased chip removal and the accuracy of hole location. Micro-drill wear was inclined to cause nail heads and decrease the accuracy of hole location.     

Characterizing mechanical behaviors of a flexible AMOLED during the debonding process

The stress distribution of a flexible active-matrix organic light-emitting diode (AMOLED) display during the debonding process was investigated using finite element analysis. During the fabrication of an AMOLED display, an AMOLED with a polyimide (PI) substrate is detached from a glass carrier; this is a critical process and generally results in failure of the AMOLED. To enhance the yielding rate of AMOLEDs, their stress states generated during the debonding process must be reduced. The interfacial fracture behavior between the PI substrate and glass carrier was characterized on the basis of bimaterial fracture mechanics, and the fracture toughness associated with mode mixity determined through peeling tests was considered a criterion for detaching the AMOLED from the glass carrier. The stress distribution of the AMOLED at the inception of debonding crack extension was evaluated according to fracture toughness. In addition, the parameters possibly influencing the stress states of the AMOLED in the debonding process are discussed.     

野外环境下陀螺全站仪定向精度与稳定性的测试与分析

基于高精度的野外地表控制网,针对不同的时间、地点和温度变化环境以及振动变化环境等实际的野外观测条件,对HGG05型陀螺全站仪的稳定性和指北定向精度进行测试与研究,通过多个周期测试数据的分析,总结出了一套方法可行、成果可靠的陀螺全站仪测试方法与数据处理程序。     

Process Mechanics of Low Plasticity Burnishing of Nitinol Alloy

Nitinol alloys have received considerable attention in biomedical and aerospace applications. Surface integrity of Nitinol devices by various manufacturing processes is crucial for their functionality. Low plasticity burnishing (LPB) is very promising to modify surface integrity due to its unique capability to adjust material properties down to the deep subsurface on the order of a few millimeters. Burnishing mechanics is essential to understand its effect on surface properties. The depth and width of burnished surface materials are characterized. A three-dimensional finite element simulation has been developed to incorporate the superelastic mechanical behavior of Nitinol. The simulation predictions are validated with the experimental results. The contact stresses, residual stresses, and strain profiles are investigated to better understand burnishing mechanics.     

Environmental and individual exposure to secondhand aerosol of electronic cigarettes in confined spaces: Results from the TackSHS Project†

Secondhand electronic cigarette (e-cigarette) aerosol (SHA) might impair indoor air quality and expose bystanders. This study aims to investigate exposure to SHA in controlled conditions of enclosed settings simulating real-world scenario. An experiment was performed in a car and in a room, in which SHA was generated during a 30-minute ad libitum use of an e-cigarette. The experiment was replicated on five consecutive days in each setting. We measured PM_2.5, airborne nicotine concentrations, and biomarkers of exposure to SHA, such as nicotine metabolites, tobacco-specific nitrosamines, propylene glycol, and glycerol in bystanders’ saliva samples before, during, and after the exposure period. Self-reported health symptoms related to exposure to SHA were also recorded. The results showed that the highest median PM_2.5 concentration was recorded during the exposure period, being 21 µg/m³ in the room setting and 16 µg/m³ in the car setting—about twofold increase compared to the baseline. Most concentrations of the airborne nicotine and all biomarkers were below the limit of quantification in both settings. Bystanders in both settings experienced some short-term irritation symptoms, expressed as dry throat, nose, eyes, and phlegm. In conclusion, short-term use of an e-cigarette in confined spaces increased indoor PM_2.5 level and caused some irritation symptoms in bystanders.     

Low molecular weight PEI-grafted carboxyl-modified soybean protein as gene carriers with reduced cytotoxicity and greatly improved transfection in vitro

SA-SP-PEI were synthesized via acylation reaction between carboxyl-modified soybean protein (SA-SP) and branched polyethylenimine (PEI) with molecular weight of 600, 1200, and 1800?Da, and designed as SA-SP-PEI600, SA-SP-PEI1200, and SA-SP-PEI1800, respectively. SA-SP-PEI could effectively condense plasmid DNA into nanoscale polyplexes and protect them from enzymatic digestion. MTT assay revealed that SA-SP-PEI exhibited reduced cytotoxicity on 293?T and SH-SY5Y cells. SA-SP-PEI1800/DNA complexes hold highest transfection efficiency on 293?T and SH-SY5Y cells with or without 10% serum, which was owing to its better serum stable and improved biocompatibility. Such polycationic soybean proteins have great potentials as gene carriers by further optimization.