Measurement of a reciprocal four-port transmission line structure using the 16-term error model

A new method to measure reciprocal four-port structures, using a 16-term error model, is presented. The measurement is based on 5 two-port calibration standards connected to two of the ports, while the network analyzer is connected to the two remaining ports. Least-squares-fit data reduction techniques are used to lower error sensitivity. The effect of connectors is deembedded using closed-form equations. (C) 2007 Wiley Periodicals, Inc.

Study of the capacitance coupling in accelerators

The relation between the input impedance and the characteristic parameters of a cavity, such as the resonance frequency, shunt impedance and. the quality factor, has been obtained based on the equivalent circuit of the cavity and the coupling system. Using the matching condition, the ratio of coupling capacitance to the equivalent capacitance of the cavity can be acquired as a function of the characteristic parameters of the cavity, the value of the coupling capacitance can be obtained with a help of a numerical simulation and the perturbation theory, and then the perfect matching between the cavity and the transmission line can be procured. The application of these results on a model cavity is presented too.

一种输电线路巡检机器人控制系统的设计与实现

介绍了一种超高压输电线路巡检机器人控制系统的设计与实现方法.根据巡检作业任务的要求,采用遥控与局部自主相结合的控制模式实现巡检机器人沿线行走及跨越障碍.设计了巡检机器人有限状态机模型,实现了机器人遥控与局部自主控制的有机结合.采用基于激光传感器定位的方法实现了巡检机器人的自主越障控制.实验结果表明,该机器人可实现沿线行走及自主跨越障碍,从而验证了控制系统设计的有效性与合理性.

基于视觉伺服的输电线巡检机器人抓线控制

巡检机器人在越障时,需要完成机器人手臂的准确抓线控制.结合输电线的几何特征和摄像机成像原理,提出了一种基于单摄像机的立体视觉方法来确定输电线的位置和姿态.基于该定位方法及视觉伺服理论,建立机械手抓线伺服控制模型.利用自行研制的巡检机器人进行了视觉伺服抓线实验;实验结果验证了该方法的有效性.

计及轴向压力的方管节点塑性铰线模型

塑性铰线分析模型已成功用于估计由弦杆表面屈服控制的各种管节点的强度；然而弦杆自身的轴向压力对节点承载力的影响仍然是用一个经验折减系数来考虑的．为了计算在轴向压力作用下沿倾斜塑性铰线的极限弯矩，研究者们提出了各种理论模型．该文对这些模型进行了分析和对比．结果表明，采用简化假设的阶梯形塑性铰线模型用于评价T形方管市点的慢度与试验结果和有限元计算结果符合得最好．

树突状细胞与 HIV-1 辅助蛋白相互作用的体外研究——细胞系模型研究价值的验证和新的研究方向的确立

树突状细胞（Dendritic cells，DCs）作为人类免疫缺陷病毒（Human Immunodeficiency Virus，HIV）感染的第一靶细胞和第一道防线， 在HIV-1感染 和传播过程当中发挥重要的功能。DC的免疫功能主要包括抗原的捕获、加工、 递呈并激活T细胞对HIV-1作出免疫反应，这些功能的发挥依赖于其自身接受刺 激有效地分化和成熟。 与其它慢病毒（lentivirus）相同，HIV-1所具有的6种辅助蛋白（Nef，Rev， Tat，Vif，Vpr和Vpu），决定着病毒自身的复制增殖和对机体的感染和致病力。 目前，HIV-1辅助蛋白对CD4+ T细胞影响的研究较为深入，是否影响和调节DC 的分化和成熟尚不够清楚，现有的文献报道很少，且相互不一致甚至矛盾。因此， 建立合适的体外研究体系和细胞模型，有针对性地进行研究DC与HIV-1之间的相 互作用，将有助于加深对HIV/AIDS致病和发病机理的理解，具有重要的生物医 学意义。 本实验选择了可被HIV-1感染的白血病细胞系THP-1为实验模型，首先评价 了THP-1作为DC前体在研究DC分化、成熟中的可用性，特别是判定DC分化成熟 和功能状态的主要细胞表面标记的动态变化和规律。进而在相同条件下分析了6 个辅助蛋白基因对THP-1的凋亡诱导作用，证实了Nef和Tat确可诱导转染细胞自 身凋亡，而Rev和Vpr可在THP-1细胞中持续表达，形成了稳定的细胞系，为进一 步研究和比较Rev、Vpr对DC的分化、成熟的影响奠定了实验基础。更重要的是， 我们发现，Vif和Vpu不能在THP-1中有效表达，其原因可能直接与限制性因子 APOBEC3G的存在有关，提示Vpu与APOBEC3G可能存在着新的相互作用——这 一线索已作为实验室新的研究方向，进一步深入的研究可能为HIV/AIDS致病、 发病机理和机体的抗病机制提供新的科学依据。

Coherent transport through a quantum dot embedded in a double-slit-like Aharonov-Bohm ring

Coherent transport through a quantum dot embedded in one arm of a double-slit-like Aharonov-Bohm (AB) ring is studied using the Green's function approach. We obtain experimental observations such as continuous phase shift along a single resonance peak and sharp inter-resonance phase drop. The AB oscillations of the differential conductance of the whole device are calculated by using the nonequilibrium Keldysh formalism. It is shown that the oscillating conductance has a continuous bias-voltage-dependent phase shift and is asymmetric in both linear and nonlinear response regimes.

A new structure of In-based ohmic contacts to n-type GaAs

Electrical, structural and reaction characteristics of In-based ohmic contacts to n-GaAs were studied. Attempts were made to form a low-band-gap interfacial phase of InGaAs to reduce the barrier height at the metal/semiconductor junction, thus yielding low-resistance, highly reliable contacts. The contacts were fabricated by e-beam sputtering Ni, NiIn and Ge targets on VPE-grown n(+)-GaAs film (approximate to 1 mu m, 2 x 10(18) cm(-3)) in ultrahigh vacuum as the structure of Ni(200 Angstrom)/NiIn(100 Angstrom)/Ge(40 Angstrom)/n(+)-GaAs/SI-GaAs, followed by rapid thermal annealing at various temperatures (500-900 degrees C). In this structure, a very thin layer of Ge was employed to play the role of heavily doping donors and diffusion limiters between In and the GaAs substrate. Indium was deposited by sputtering NiIn alloy instead of pure In in order to ensure In atoms to be distributed uniformly in the substrate; nickel was chosen to consume the excess indium and form a high-temperature alloy of Ni3In. The lowest specific contact resistivity (rho(c)) of (1.5 +/- 0.5)x 10(-6) cm(2) measured by the Transmission Line Method (TLM) was obtained after annealing at 700 degrees C for 10 s. Auger sputtering depth profile and Transmission Electron Microscopy (TEM) were used to analyze the interfacial microstructure. By correlating the interfacial microstructure to the electronical properties, InxGa1-xAs phases with a large fractional area grown epitaxially on GaAs were found to be essential for reduction of the contact resistance.

输电线巡检机器人行走动力特性与位姿分析

根据跨越超高压输电线路障碍物的类型,提出一种新的双臂自主越障巡检机器人机构。该机器人采用复合轮爪机构在架空地线上连续行走并跨越障碍。由于架空地线呈悬链线状,机器人在连续行走过程中会出现上坡和下坡,对行走动力特性的影响非常明显。在上坡时行走电动机提供驱动力矩,在下坡时行走电动机提供制动力矩,以保持匀速巡线。详细分析了机器人在架空地线上行走时所处的加速、匀速、减速和停止的各个状态,驱动机器人所需的驱动力矩以及它们与机构参数之间的关系,并应用优化方法给出各个状态电动机驱动力矩最小时,机器人机构参数对应的最优解,为巡检机器人的设计和控制系统方案的确定提供了理论依据。

一种自主越障巡检机器人行走夹持机构

在机器人越障过程中,由于重力的影响使得机器人车体水平姿态发生变化,从而机器人自主越障变得十分困难。分析了超高压输电线路障碍物的类型,提出了一种新的双臂自主越障巡检机器人构型,该构型能够跨越输电线路上的障碍物。针对这种新构型,阐述了机器人行走夹持机构的工作原理和实现形式,着重分析研究了偏心夹持机构对保持车体水平姿态的机理。最后,通过越障实验验证了行走夹持机构的可行性。

基于分布式专家系统的超高压输电线路巡检机器人控制系统的研究

探讨了基于分布式专家系统的超高压输电线路巡检机器人控制系统，给出了一种利用CUPS和C、VC++混合编程构成分布式专家系统作为机器人控制器的方法，并且提出了一种基于规则和证据的可信度(CF)的分布式专家系统的协调算法．经过试验论证，该控制方法能很好地实现超高压输电线路巡检机器人的作业功能。

输电线巡检机器人控制与实验研究

近年来，机器人的应用越来越广泛和深入，输电线巡检机器人是当前特种作业机器人的研究热点之一，具有广泛的应用前景和实用价值。本文的研究内容是围绕国家“863”计划支持项目“500KV超高压输电线巡检机器人的研究”展开的。本研究工作针对巡检机器人的关键控制问题，主要由三部分组成：设计了巡检机器人的体系结构，并应用离散事件理论对机器人的任务、行为和动作建模；对巡检机器人双轮同步驱动控制进行了分析，并应用奇异摄动理论设计了控制器；研究了基于单目视觉的输电线立体定位方法及通过视觉伺服完成机器人自主抓线控制。 第一，介绍了巡检机器人的作业环境，重点探讨了机器人机械系统和控制系统的设计与实现。在机械子系统中，详细介绍了巡检机器人的机构实现与越障方法。在控制系统中详细阐述了基于分层递阶的机器人控制系统硬件组成。另外介绍了供电系统、无线传输系统、传感系统的设计与实现。分析了输电线路周围的电磁环境，及其对机器人的影响，并根据分析结果完成了对机器人的电磁防护设计。 第二，开展了输电线巡检机器人体系结构及人机交互系统研究，针对巡检机器人工作特点设计了基于规划和感知行为的混合式体系结构。针对巡检机器人工作环境设计了以机器人为中心的人机交互方式。参考前人建立的离散事件动力系统的层次结构和并行结构，提出了顺序结构并证明了其无阻塞性、可控性和监控器存在性，并结合以上三种结构建立了巡检机器人作业行为的离散动力学模型，分别获得了任务层、行为层和动作层的监控器。 第三，进行了巡检机器人双轮驱动控制研究。巡检机器人双轮行走机构为过驱动系统，对双轮行走系统进行了运动学和动力学建模，将一行走轮设为主动轮另一行走轮设为从动轮。针对两行走轮之间弹性关节导致的控制中的振荡问题，采用奇异摄动理论将系统分为快慢两个子系统；针对巡检机器人系统参数的时变性采用PD自适应算法设计了慢系统控制器；应用最优控制理论设计了快系统控制器。仿真结果验证了该方法的有效性。 第四，进行了输电线视觉定位和视觉伺服抓线问题的研究。输电线巡检机器人的自主越障控制是实现机器人实用化的关键问题。为实现巡检机器人自主越障，采用视觉伺服控制机械手臂自动抓线。为提取输电线图像特征点，针对输电线投影图像特征改进了边缘提取算法，应用聚类算法提取了输电线上的像素点。提出在机械手运动过程中采用EKF（扩展卡尔曼滤波）来实现对输电线的立体定位。在分析了当前基于图像的视觉伺服研究现状，建立了基于图像雅克比矩阵的输电线视觉伺服抓线模型。针对非标定状况下图像雅可比矩阵中的不确定参数，应用I&I(Immersion Invariant)自适应算法来实现无标定图像视觉伺服。针对机器人的动力学不确定性，设计了模糊自适应控制器，并证明了稳定性。仿真验证该方法的有效性，实验验证了基于视觉伺服的抓线控制的有效性。

Determination of ionic resistance and optimal composition in the anodic catalyst layers of DMFC using AC impedance

In the present study, a method based on transmission-line mode for a porous electrode was used to measure the ionic resistance of the anode catalyst layer under in situ fuel cell operation condition. The influence of Nafion content and catalyst loading in the anode catalyst layer on the methanol electro-oxidation and direct methanol fuel cell (DMFC) performance based on unsupported Pt-Ru black was investigated by using the AC impedance method. The optimal Nafion content was found to be 15 wt% at 75 degrees C. The optimal Pt-Ru loading is related to the operating temperature, for example, about 2.0 mg/cm(2) for 75-90 degrees C, 3.0 mg/cm2 for 50 degrees C. Over these values, the cell performance decreased due to the increases in ohmic and mass transfer resistances. It was found that the peak power density obtained was 217 mW/cm(2) with optimal catalyst and Nafion loading at 75 degrees C using oxygen. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Numerical Analysis of Theoretical Model of the Rf MEMs Switches

An improved electromechanical model of the RF MEMS (radio frequency microelectromechanical systems) switches is introduced, in which the effects of intrinsic residual stress from fabrication processes, axial stress due to stretching of beam, and fringing field are taken into account. Four dimensionless numbers are derived from the governing equation of the developed model. A semi-analytical method is developed to calculate the behavior of the RF MEMS switches. Subsequently the influence of the material and geometry parameters on the behavior of the structure is analyzed and compared, and the corresponding analysis with the dimensionless numbers is conducted too. The quantitative relationship between the presented parameters and the critical pull-in voltage is obtained, and the relative importance of those parameters is given.

Size-Dependent Interface Phonon Transmission And Thermal Conductivity Of Nanolaminates

An analytical model for size-dependent interface phonon transmission and thermal conductivity of nanolaminates is derived based on the improved acoustic mismatch theory and the Lindemann melting theory by considering the size effect of phonon velocity and the interface lattice mismatch effect. The model suggests that the interface phonon transmission is dominant for the cross-plane thermal conductivity of nanolaminates and superlattices, and the intrinsic variety of size effect of thermal conductivity for different systems is proposed based on the competition mechanism of size effect of phonon transport between two materials constituting the interfaces. The model's prediction for thermal conductivity of nanolaminates agrees with the experimental results. (C) 2008 American Institute of Physics.