Inside Cover: Bidirectional Chemo‐Switching of Spin State in a Microporous Framework (Angew. Chem. Int. Ed. 26/2009)

Bidirectional chemo‐switching of magnetism occurs in a microporous coordination polymer containing spin‐crossover subunits, as described by M. Ohba, J. A. Real, S. Kitagawa, and co‐workers in their Communication on page 4767 ff. In situ magnetic measurements reveal that most guest molecules transform the framework spin state from diamagnetic low spin (red) to paramagnetic high spin (yellow), whereas the guest CS₂ stabilizes the low‐spin state. These induced spin states are retained as a memory effect after the release of the guest.

     

Comparative analysis of availability between three systems with general repair times, reboot delay and switching failures

This paper compares the availability characteristics between three different systems with reboot delay and standby switching failures. Three systems are studied under the assumption that the time-to-failure and the time-to-repair of the primary and standby units are exponentially and generally distributed, respectively. The reboot times are assumed to be exponentially distributed with parameter β. It is assumed that there is a significant probability q of a switching failure. Using the supplementary variable technique, we develop the explicit expressions for the steady-state availability, Av, for three configurations and perform comparative analysis for three various repair time distributions, such as exponential, gamma, and uniform. Under the cost/benefit criterion, comparisons are made based on assumed numerical values given to the distribution parameters, and to the cost of the primary and standby units.     

Determination of phenolic compounds in river water with on-line coupling bisphenol A imprinted monolithic precolumn with high performance liquid chromatography

The bisphenol A (BPA) imprinted monolithic precolumn has been prepared by in situ polymerization using 4-vinylpyridine (4-VP) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. The column with good flow-through property was obtained by changing the molar ratio of the porogens (toluene and dodecanol). The selectivity and retention properties of the monolith for the BPA and other phenolic compounds were evaluated. The results show that the hydrophobic and hydrogen-bonding interaction plays important roles in the recognition process. The determination of BPA and other phenolic compounds with on-line solid-phase extraction (SPE) by monolithic precolumn coupled with conventional particulates packed and monolithic reversed-phase columns, respectively, was performed. The method was successfully applied to the analysis of phenolic compounds in river water.     

Diarylethenes with intramolecular donor-acceptor structures for photo-induced electrochemical change

Diarylethenes with donor-acceptor groups were synthesized to induce electrochemical switching by light. Photoisomerization was induced by 1,2-bis(2-methyl-1-benzo[b]thiophen-3-yl)perfluorocyclopentene (BTF, 1) unit, while the 3,4-ethylenedioxythiophene (T) and nitro (N) groups were directly connected to BTF, to extend π-electron delocalization. Spectral change to a longer wavelength through photochromism was significant in the donor-acceptor structures (6), accompanied by an increase in the molar absorption coefficients, than those of the unsubstituted BTF (1) or the BTF substituted with only acceptor group (2c and 3c). A significant peak shift toward lower redox energy was observed when the molecules were converted from an open isomer to a closed isomer. The plot of the reduction potentials ((E_1/2^red, V vs Ag/AgCl) vs LUMO energy eV) for the diarylethenes indicates that the reduction potential is strongly dependent on the nature of the substituents around the diarylethene unit. When 6 was applied to a photocell of Au/PC/ITO glass, in which PC is the polystyrene containing 6, it became possible to switch the conductivity of the cell through the film by UV-vis irradiation, as estimated by the I-V plot on a photocell. The conductivity of the cell exposed to UV light was three times larger than that of the cell exposed to visible light, and 10 times larger than that of the cell containing 3, indicating the importance of the push-pull structure for π-electron connectivity through the donor-BTF-acceptor.     

直流环节逆变器的相平面分析及软开关条件研究

 新型谐振直流环节逆变器具有PWM和软开关双重优点,然而辅助谐振直流环节有4个换能元件,使逆变器具有复杂的动力学行为和高维时变特性,用解微分方程的方法研究系统的动态特性和求解软开关条件及设计规则是相当复杂和困难的.结合相平面法分析的特点,该文将4维电路分解在3个相平面研究了系统的动力学行为、软开关条件以及设计规则.文中详细阐述了相平面的构建和分析过程,利用相平面分析结果和解析几何方法求取了软开关条件及设计规则.利用设计规则,搭建了逆变器驱动无刷直流电机的实验,实验结果验证了相平面分析的正确性和设计规则的可行性.     

Effect of post annealing on the resistive switching of TiO2 thin film

The effect of annealing on the resistive switching of 35-nm-thick TiO₂ thin film deposited with magnetron sputtering system was studied. Pt and Ag were used as a top electrode (TE), and Pt was used as a bottom electrode (BE). For Pt/as-deposited TiO₂/Pt structure, both unipolar (URS) and bipolar resistive switching (BRS) were observed depending on the current compliance level. For Pt/400 °C annealed TiO₂/Pt structure, only BRS was observed regardless of the current compliance level. The increase in the work function of the TiO₂ film after annealing lowers the potential barrier height and changes the electron transfer process which was also confirmed from Ag/as-deposited TiO₂/Pt structure. Above 600 °C, the film becomes leaky with the increase in grain size and roughness and the resistive switching behavior was not observed.     

一种适用于DC/DC开关电源芯片的锯齿波振荡器设计

应用于手机等通信电子产品电源系统的DC/DC开关电源变换器芯片,要求具有高性能的锯齿波振荡器.鉴于此要求,设计了一款具有级冲放电电容的高性能锯齿波振荡器.基于华润上华CSMC 0.5 μmBiCMOS工艺库,利用Cadence Spectre软件进行电路仿真,在芯片系统典型应用环境下仿真得到锯齿波振荡频率为5 MHz,信号幅值为0～3 V.频率随电源电压在2.7～5.5 V变化范围和温度在-20～100 ℃变化范围而产生的偏移在±4%以内.该锯齿波振荡器的性能良好,已经成功应用于一款DC/DC降压开关电源芯片的设计之中.     

基于MPLS的流量工程仿真

多协议标签交换（MPLS）技术的成熟和扩展将推进基础网络的智能化和下一代光网络的实现。在对流量工程和MPLS体系结构分析的基础上,讨论了利用MPLS实现流量工程的优势。利用网络仿真器NS2设计了OSPF（开放最短路径优先）路由协议和MPLS流量工程的实例。通过对仿真结果的比较和分析,可以看出MPLS流量工程可以有效地实现网络负载均衡和恢复机制,提高网络服务质量。     

大功率单片开关电源的设计

提高电路的集成化是开关电源的追求之一.同样的功率,希望电源更轻小,电路更简单,采用元件器更少,性价比更高,单片开关电源就具备这些优点.文中基于PI公司的TOP249Y设计了一款大功率的单端反激式的单片开关电源,介绍了TOPswitch-GX的内部结构和引脚功能,给出了实用电路并分析了其工作原理,并结合PI公司的PI Expert 7.0软件设计出了关键元件变压器.测试结果表明,该电源额定输出功率为250 W,效率不小于85%,空载功耗不大于1.4 W.     

电子辐照对绝缘栅双极晶体管开关速度的影响

The influence of electron irradiation on the switching speed in insulated gate bipolar transistors（IGBT） with different epitaxial layer thicknesses is discussed in detail.The experimental results prove that the fall time of IGBT increases when increasing the thickness of the epitaxial layer.However,there is no obvious difference between the ratios of the fall time after irradiation to those before irradiation for different epitaxial layer thicknesses.The increase in switching speed of the IGBT is accompanied by an increase in the forward drop,and a trade-off curve between forward voltage drop and fall time of IGBT is presented.