The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part III. Potential dependent current

The potential dependence of the steady-state current at a channel electrode has been calculated approximately. Six regions of behavior can be described from a consideration of the characteristic times of diffusion, fluid flow and electrochemical reaction. Wave shapes and half-wave potential shifts are as expected for amperometric cells under all values of the heterogeneous reaction rate constant, and for reversible electrochemical reactions in a coulometric cell. The wave adopts a peculiar shape for irreversible reactions at a coulometric electrode. This is caused by the inapplicability of the concept of mass transfer control in these systems.     

Translocation of Ca2+ across lipid bilayer membrane due to defects induced by teleocidin

The effect of defects in a dipalmitoylphosphatidylcholine (DPPC) membrane on Ca²⁺ permeability across the membrane was studied. Addition of teleocidin to a suspension of DPPC vesicles encapsulating Quin 2 increased the fluorescence intensity of Quin 2. Change of fluorescence intensity was significant below the phase-transition temperature of the membrane, and increased according to the kind of divalent metal ions in the medium in the order of Mg²⁺2+2+. It was confirmed that DPPC vesicles did not change the vesicular structure upon binding teleocidin to the membrane. Therefore, the fluorescence increase below the phase-transition temperature was ascribed to the influx of divalent cations into DPPC vesicles through cracks formed in the membrane upon distribution of teleocidin. By contrast, 12-0-tetradecanoylphorbol-13-acetate (TPA) did not change the fluorescence intensity of Quin 2 significantly. It should be noted that teleocidin, which located at the membrane surface, yielded more significant defects across the lipid membrane than TPA, which was incorporated into the hydrophobic core of the membrane.     

Substitution effects on the molecular structures and the longitudinal molecular polarizabilities of all‐trans polyacetylene oligomers of increasing size

AM1 calculations have been performed on all‐trans polyacetylene (PA) oligomers with an increasing number of unit cells to study the effect of donor or acceptor groups capped at opposite ends of PA chains, substituents included in the monomers, substituents' number and position in the monomers, on the molecular structures, and the static longitudinal polarizabilities (α_L) and second‐order hyperpolarizabilities (γ_L). Substitution of CH₃, Cl, or F group at opposite ends of an oligomer results in an increase of α_L and γ_L, but the substitution effects on Δα_L(N) and Δγ_L(N) are very small. The asymptotic limit values are unaffected by the substitution. F substituent included in the monomer of an oligomer enhances the Δα_L(N) and Δγ_L(N) values, especially at large N, but including monomers with CH₃ or Cl substituents substantially reduces the Δα_L(N) and Δγ_L(N) values. We alter the number of F substituents included in the monomers of oligomers and find that including two F substituents in the monomer leads to the larger enhancement of Δγ_L(N). The effect of F substituents' position in the monomers of oligomers on Δα_L and Δγ_L is obvious. The results may be helpful for the design of new materials for applications in nonlinear optics, particularly in the area of poled polymer films. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

A Fully Integrated Class 1 Bluetooth 0.25 μm CMOS PA

A fully integrated 0.25 m CMOS bluetooth class 1 power amplifier is presented. On this chip all inductors and decoupling capacitors are situated on the silicon die. Due to the high level of integration, a cheap flip chip assembly method has been used. The chip delivers 138 mW (21.4 dBm) of output power with a power added efficiency of 25.8%. When the amplifier is tuned to its optimum frequency of 2.1 GHz, the output power increases to 184 mW and the power added efficiency increases to 29.5%. To compare the performance of this realisation with other recently published PA, a figure of merit for saturated (switched) power amplifiers is introduced.Koen Mertens was born in Antwerpen, Belgium in 1971. He received the M.Sc. degree in Electrical Engineering from the Katholieke Universiteit Leuven, Belgium in 1998. The subject of his M.Sc. thesis was the design of a 2.14 GHz BICMOS oscillator. The thesis was in cooperation with IMEC. Since 1998. He has been a research assistant at the ESAT-MICAS laboratories, where he is currently working towards a Ph.D. degree in CMOS RF Power Amplifiers. His research promotor is Prof. Michiel Steyaert.Michiel Steyaert Michel S.J. Steyaert was born in Aalst, Belgium, in 1959. He received the masters degree in electrical-mechanical engineering and the Ph.D. degree in electronics from the Katholieke Universiteit Leuven (K.U. Leuven), Heverlee, Belgium in 1983 and 1987, respectively.From 1983 to 1986 he obtained an IWNOL fellowship (Belgian National Fundation for Industrial Research) which allowed him to work as a Research Assistant at the Laboratory ESAT at K.U. Leuven. In 1987 he was responsible for several industrial projects in the field of analog micropower circuits at the Laboratory ESAT as an IWONL Project Researcher. In 1988 he was a Visiting Assistant Professor at the University of California, Los Angeles. In 1989 he was appointed by the National Fund of Scientific Research (Belgium) as Research Associate, in 1992 as a Senior Research Associate and in 1996 as a Research Director at the Laboratory ESAT, K.U. Leuven. Between 1989 and 1996 he was also a part-time Associate Professor. He is now a Full Professor at the K.U. Leuven. His current research interests are in high-performance and high-frequency analog integrated circuits for telecommunication systems and analog signal processing.Prof. Steyaert received the 1990 European Solid-State Circuits Conference Best Paper Award, the 1995 and 1997 ISSCC Evening Session Award, the 1999 IEEE Circuit and Systems Society Guillemin-Cauer Award and the 1991 NFWO Alcatel-Bell-Telephone award for innovative work in integrated circuits for telecommunications.     

基于0.13μm CMOS的WiFi功率放大器设计

基于TSMC 0.13 μm CMOS工艺,设计了一款适用于无线保真(WiFi)收发机的发射端、工作在2.4 GHz且增益可控的三级级联功率放大器.驱动级采用单管结构,后两级采用共源共栅(MOSFET)结构.利用调节共源共栅晶体管栅极的电容来改变栅极电压的相位,进而弥补了共源共栅结构的劣势,增加了整个系统的线性度和增益.另外,使用外部数字信号控制每级偏置的大小来适应不同的输出需求.整个结构采用电源电压:第一级为1.8V,后两级为3.3V,芯片面积为1.93 mm×1.4 mm.利用Candence Spectre RF软件工具对所设计的功率放大器进行仿真.结果表明,在2.4 GHz的工作频点,功率放大器的饱和输出功率为24.9 dBm,最大功率附加效率为22％,小信号增益达到28 dB.     

功率挖掘提升农村LTE网络驻留能力方案

前农村LTE基站大都基于GSM站点共址建设,站间距较大,无法满足连续覆盖和深度覆盖的需求,导致用户弱覆盖投诉较多,本文结合农村覆盖场景特点,通过RS Power Boosting、10M组网手段挖掘LTE功率提升农村区域LTE网络驻留能力。     

The influence of polypyrrole coatings on the mechanical and friction and wear properties of bamboo fiber filled PA6 composites

The effects of polypyrrole coatings on the tensile and tribological properties of bamboo fiber reinforced polyamide 6 (PA6) composites were studied. Tribological tests were conducted using a block‐on‐ring arrangement. It was observed that the polypyrrole coatings played a main role in the tensile‐resistant and wear‐resistant properties of the PA6 composites. The tensile properties were ruled by the fiber‐matrix adhesion. And the excellent tribological performance of the fillers improved the tribological properties of PA6 composites. The optimum content of polypyrrole coating concentration is 7vol%.     

一种用于5G 终端的毫米波收发器前端芯片的研制

用0.15 μm GaAs 增强型赝配高电子迁移率电子管(EPHEMT)工艺研制了一款集功率放大器、低噪声放大器、单刀双掷开关为一体的、可用于5G 宽带无线移动通信系统终端的毫米波收发器前端芯片。其中,功率放大器采用电抗匹配技术的两级放大拓扑结构,单刀双掷开关采用正电压控制的对称器件结构,低噪声放大器采用两级最佳噪声兼顾增益的拓扑结构。测试结果表明, 24.25 ~ 27.5 GHz频带内,芯片发射支路饱和输出功率>22 dBm,附加效率>28%;芯片接收支路噪声系数<3.0 dB, 线性增益>13 dB; 芯片收发隔离度优于-20 dB。该芯片面积为2.2 mm×1.8 mm。     

交响音乐会扩声与电视录音探讨

本文以交响音乐会在非音乐厅演出的情况下,在需要扩声的同时,兼顾电视录音出发,与读者共同探讨,交响音乐会的现场扩声与电视录音的艺术处理。     

High performance long chain polyamide/calcium silicate whisker nanocomposites and the effective reinforcement mechanism

PA1012/calcium silicate whisker nanocomposites with contents of whisker ranging from 10 wt% to 40 wt%, are prepared by twin screw extruder without any additions of coupling agent. The effect of whisker on the matrix is analyzed by the studies of morphology, the mechanical properties, water absorption and thermal stabilities. SEM micrographs obviously demonstrate, even under the high filler content of 40 wt% and without surface treatment, calcium silicate whisker can be homogeneously dispersed in polyamide, directly leading to the enhanced mechanical properties. The mechanism of higher efficiency of reinforcement is needle-like shape whisker, having access to be intercalated, and mutual affinity caused by hydrogen bonding interaction between carbonyl group in polyamide chain and hydroxyl group in whisker surface. Both aspects attach matrix with excellent stress-transfer properties. In addition, with the assistance of whisker, the nanocomposite favors an improved water absorption as well as thermal stability, which is intimately associated with physical performance.