Electron transfer reactions of glucose oxidase at Au111 electrodes modified with phenothiazine derivatives

The catalytic reaction of glucose oxidase (GOx) mediated by 3-(10-phenothiazyl)propionic acid (PT-PA) and phenothiazine-labeled poly(ethylene oxide) (PT-PEO1000) that are covalently bonded to Au(111) electrodes has been investigated. The PT-PA and PT-PEO1000 are reacted with 2-aminoethanethiol (AET), followed by the formation of a self-assembled monolayer (SAM) onto the Au surface. The PT group immobilized on the SAM of AET acts as an effective mediator for the electron transfer (ET) between the electrode and the FAD center of freely diffusing GOx in solution. The ET rate constant estimated from the catalytic current using a newly derived equation is larger by 1 order of magnitude for the PT-PA-modified system (1.1 x 10(5) dm(3) mol(-1) s(-1)) than for the PT-PEO1000 system (1.4 x 10(4) dm(3) mol(-1) s(-1)). The order of the magnitude of the ET rate constant clearly contrasts with the GOx hybrid systems that we previously investigated (Anal. Chem. 2003, 75, 910-917), in which the presence of the PEO spacer enhances the ET reaction rate. The reduction in the apparent PT concentration at the electrode interface due to the high mobility of the PEO chain, leading to low efficiency in the formation of an enzyme-mediator complex, is a possible reason for the lower mediation ability of PT-PEO1000 than that of PT-PA for the ET between the FAD group and PT(+) immobilized on the electrode. Inhibition of the penetration of GOx molecules into the monolayer and of the accessibility of some part of PT groups to GOx molecules could also be reasons for the lower mediation ability of PT-PEO1000 thickly modified on the electrode.     

New Class of High-TC Diluted Ferromagnetic Semiconductors Based on CaO without Transition Metal Elements

We propose new-type ferromagnetic semiconductors based on CaO and K₂S without any transition metal elements. These materials show transparent and half-metallic ferromagnetism if the deep-impurity-band width (W) induced by doping of C, N, Si, or Ge impurities, and the electron-correlation energy (U) satisfy the Stoners condition of highly correlated electron system (U>W). Based on our first-principles calculations, we demonstrate that these materials satisfy the Stoners condition, and could be new candidates for transparent and half-metallic DMSs.     

New Class of High-<Emphasis Type="Italic">T</Emphasis><Subscript>C</Subscript> Diluted Ferromagnetic Semiconductors Based on CaO without Transition Metal Elements

We propose new-type ferromagnetic semiconductors based on CaO and K₂S without any transition metal elements. These materials show transparent and half-metallic ferromagnetism if the deep-impurity-band width (W) induced by doping of C, N, Si, or Ge impurities, and the electron-correlation energy (U) satisfy the Stoner’s condition of highly correlated electron system (U>W). Based on our first-principles calculations, we demonstrate that these materials satisfy the Stoner’s condition, and could be new candidates for transparent and half-metallic DMSs.     

Direct imaging of molecular chains in a poly(p-xylylene) single crystal

Individual chains comprising a β-form poly(p-xylylene) (PPX) single crystal were resolved with a high resolution electron microscope (JEM-500). In a polymer crystal the important limiting factor for resolution is radiation damage. The total end point dose of a PPX crystal is about 0.5 coulomb cm^?2 for 500 kV electron irradiation which is more than 20 times greater than that for a polyethylene crystal. The high resolution image obtained was processed by optical filtering to reduce noise due to the granularity of film. The processed image, which corresponds to the ab-plane projection of polymer chains, shows clearly the mutual arrangement of each molecule in the crystal. This high resolution image is sufficient to provide a starting point for determining the unknown crystal structure of the β-modification of PPX.     

Heat capacity of metallic uranium and thorium from 80 to 1000 k

The heat capacities of metallic uranium and thorium from 80 to 1000 K have been determined by laser-flash calorimetry. The results on uranium agree very well with those in the literature over the temperature range investigated. The results on thorium are several percent lower than the heat-capacity values hitherto reported, while the enthalpy data at high temperatures in the literature are in good agreement with the present results. Shomate's analysis showed that the present results are the most consistent through the temperature range from 80 to 1000 K. On this, a revised table of thermodynamic functions of thorium from 80 to 1000 K is presented. The excess heat capacity on thorium has been found to be not appreciable up to 1000 K, in contrast with the large excess heat capacity above 300 K for uranium.     

多几何要素影响下液压阀件特性的混合神经网络预测模型

液压阀件系统是一个具有多几何要素影响的多系统特性复杂系统,建立液压阀件特性预测模型,以系统多几何要素作为输入,实现系统特性的预测,将对实际生产具有重要的意义。在深入分析反向传播(Back propagation,BP)神经网络与径向基函数(Radial basis function,RBF)神经网络的基础上,结合两类神经网络的特点,提出基于BP神经网络与RBF神经网络的混合神经网络预测模型。利用生产实际中实测的某具体液压阀件特性值及影响该特性的各几何要素值作为预测模型的数据来源,对所提出的混合神经网络进行训练,并进行仿真。实例计算表明混合神经网络预测模型可提高单项神经网络预测模型的预测精度,预测平均相对误差为0.0461。可见,所提出的混合神经网络预测模型能够很好地满足工程实践中液压阀件特性预测要求。     

采用电荷泵箝位调整器的BUCK型DC-DC驱动电路

为了提高驱动效率,设计了一种新颖的适用于BUCK型DC-DC的驱动电路,在芯片内部采用一个电荷泵和自适应死区时间控制逻辑的驱动电路。当芯片正常工作时,输出级低端LDNMOS管的驱动电平通过较大的电荷泵电容稳定在5.5V左右,输出级高端LDNMOS管的驱动电平通过自举电容高达29.93V,从而实现对DC-DC输出级高端和低端的驱动,这样既提高了驱动效率,又减少了对外部多个电源的需求。采用此电路的一款电流模BUCK型DC-DC已在UMC06μmBCD工艺线投片,芯片效率高达94%,输出级高端和低端LDNMOS的导通电阻为120mΩ,最大输出电流为5A,该驱动电路工作良好,芯片面积减小了15.4%。     

Researches on the computer digital control system of giant magnetostrictive actuator

In this paper, a computer digital control system of giant magnetostrictive actuator (GMA) was designed. In GMA system, driving magnetic field was provided by variable magnetic field generated by exciting coil current and offset magnetic field generated by permanent magnet. And Terfernol-D was used as the giant magnetostrictive materials (GMM). GMA’s control model was analysed and the whole control system was established. In the computer digital control system, the control core were single-chip microcomputer and PC with modularization thinking. And the control algorithm was PID. Design for system’s hardware and software was completed and software package was developed. Experiment shows that the GMA system is controlled automatically and monitored real-time. It lays a foundation of further improving control precision of GMA, improving the entire system’s dynamic characteristics and realizing automatic control.     

自适应开启时间的电流模Buck控制器

设计了一种基于自适应开启时间（Adaptive On-Time, AOT）控制的电流模buck型DC-DC控制器电路,利用输入电压前馈和输出电压反馈技术来获得开启时间,并提出了一种采样保持和充电时间超前电路实现了开启时间的自适应控制。电流模AOT控制不仅获得了优异的瞬态响应速度,而且克服了电压模开启时间控制的环路稳定性对输出电压纹波的依赖。电流模AOT控制无固定频率峰值电流控制中的亚谐波振荡问题,不需要斜坡补偿。自动跳跃式（Auto-Skip）脉冲频率调制（Pulse Frequency Modulation, PFM）模式有效地改善了轻负载下的转换效率。芯片采用UMC 0.6-μm BCD工艺投片验证,文章最后给出了详细的测试结果。