Generation of uniform tetrapod-shaped zincoxide nanoparticles by gas-phase reaction with using flow restrictor

Tetrapod-shaped ZnO particles are generated via gas-phase reaction of Zn vapor and oxygen in air, where they undergo homogeneous nucleation from supersaturated ZnO vapor and successive growth by surface reaction. It was found that a simple device for flow restrictor is effective in making ZnO particles of terapod-shape by leaving sufficient amounts of unreacted Zn vapor with the embryos of ZnO. In the absence of the flow restrictor, only spherical particles are formed because the oxidation reaction takes place immediately after mixing and unreacted Zn vapor does not remain for the subsequent crystal growth. The Zn vapor concentration distribution, oxygen concentration distribution, temperature, gas velocity and reaction rate in the reactor were analyzed by using a conventional computational fluid dynamic simulation package. The simulation revealed that the flow restrictor does not enhance mixing between Zn vapor and air but suppresses the mixing and reduces the residence time in the reactor so that sufficient amounts of unreacted Zn vapor remain downstream of the flow restrictor, allowing ZnO particles to grow in tetrapod-shape by abnormal crystal growth.     

Functional expression of horseradish peroxidase in Saccharomyces cerevisiae and Pichia pastoris

The ability to engineer proteins by directed evolution requiresfunctional expression of the target polypeptide in a recombinanthost suitable for construction and screening libraries of enzymevariants. Bacteria and yeast are preferred, but eukaryotic proteinsoften fail to express in active form in these cells. We haveattempted to resolve this problem by identifying mutations inthe target gene that facilitate its functional expression ina given recombinant host. Here we examined expression of HRPin Saccharomyces cerevisiae. Through three rounds of directedevolution by random point mutagenesis and screening, we obtaineda 40-fold increase in total HRP activity in the S.cerevisiaeculture supernatant compared with wild-type, as measured onABTS [2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)](260 units/l/OD₆₀₀). Genes from wild-type and two high-activityclones were expressed in Pichia pastoris, where the total ABTSactivity reached 600 units/l/OD₆₀₀ in shake flasks. The mutantsshow up to 5.4-fold higher specific activity towards ABTS and2.3-fold higher specific activity towards guaiacol.     

Validating Operator Event Sequence Diagrams: The case of an automated vehicle to human driver handovers

Predicting what drivers will do as vehicle control is handed over to them from automation is a relatively new challenge for the motor vehicle industry. Operator Event Sequence Diagrams (OESDs) offer a way of modeling the interactions between the driver and vehicle automation in the handover of control. In this paper, two studies are presented in which a range of handover strategies are tested. The anticipated driver strategies were modeled using OESDs to serve as predictions of driver behavior. Drivers were then observed in two separate studies: (1) using a Lower-Fidelity (vehicle seat and controls) simulator and (2) using a Higher-Fidelity (whole vehicle) simulator. Driver behavior during a takeover task was categorized according to the signal detection paradigm into hits, misses, false alarms, and correct rejections. The results showed that for all strategies in both sets of studies, the median criterion for validity was exceeded ( > 0.8), suggesting that OESDs made good predictions of driver behavior during the handover of the vehicle from automation to manual control.     

定制边界滑移平行轴承的挤压效应(英文)

作者最近提出了一种利用滑块入口处的壁面滑移产生流体动压的新型轴承.笔者针对该类新轴承的油膜挤压问题,提出了基于滑移临界剪应力的数学模型,并给出了解析解.结果显示压力分布为分段光滑的抛物线,在滑移/非滑移边界,存在不连续的压力梯度.不同参数条件下的计算给出了不同的压力分布和壁面滑移类型.结果显示,对于代表滑块非浸润区长度的参数xt,最大压力并不总是随参数xt的减小而减小.存在一个参数xt的区间,在该区间内最大压力不变.与经典的挤压膜轴承类似,压力随膜厚的增加或趋进速度的减小而减小.笔者还发现临界剪应力的对挤压效应有重要的影响,揭示了此类新型轴承的一些内在的特性.