A Over A原则和劳斯制约律

在1967年以前,转换语法被用得几近万能,人们不无讥讽地说它还可以用来洗碗碟。但由于转换语法不能解释有些语言材料,人们开始疑惑起来了。     

奥迪A5

奥迪A5的面世，丰富了奥迪的产品序列，并使其拥有同竞争对手全线抗衡的本钱！一个庞大的全系列奥迪家族就此基本建立起来，就A5车型本身而言，拥有比A4、A6更加时尚的外观，比TT宽敞的多的内部空间，能够满足一部分特定人群的消费需求，市场表现不会令人失望。[编者按]     

利用D／A转换器模拟A／D转换器

介绍在单片机应用系统中利用高位D／A转换器模拟A／D转换器的方法、电路及其程序设计。     

“景区创A有了5A新标准”

据统计,2013年我国全年国内出游人数32亿人次,其中A级景区接待游客数量超过30亿人次,而规模前50位的基本上都是4A、5A级旅游景区.随着各种旅游强国、旅游强市、旅游强县概念的提出,旅游景区已日益成为带动全国旅游产业发展的主体,4A、5A等精品旅游景区更是我国旅游景区的中坚力量.     

A LESSON WITH THE TREATMENT OF A GIANT HEPATOCELLULAR ADENOMA

ＡＬＥＳＳＯＮＷＩＴＨＴＨＥＴＲＥＡＴＭＥＮＴＯＦＡＧＩＡＮＴＨＥＰＡＴＯＣＥＬＬＵＬＡＲＡＤＥＮＯＭＡＰａｎＣｈｅｎ＇ｇｅｎ（潘承恩）；ＷａｎｇＪｕｂｉｎ（王居邠）；ＬｕＹｉ（吕毅）（ＤｅｐａｒｔｍｅｎｔｏｆＨｅｐａｔｏｂｉｌｉａｒｙＳｕｒｇｅｒｙ...     

维生素A与癌

<正> 维生素A及其衍生物视黄质(retinoids),对分泌上皮的生长、分化和功能极为重要。维生素A缺乏的动物,其呼吸道,唾液腺、胰腺和前列腺的纤毛上皮和粘液分泌上皮可化生     

谈谈奥迪A1

22.48万～28.98万元,这是奥迪最新一款小型车A1的售价,对于这个售价,网友给出了各自的看法:有钱人的玩具;人生的梦想;定价太高了,不如买MINI;脑子有病买它;通货膨胀后必买的车等等。作出评价的人之中可能有的看法比较偏激,有的确实喜欢,有的结合了现在的国情。在这篇文章中,我只想用我的眼光来和大家谈谈这款"小车"。     

组合式A／D，D／A转换器的设计

组合式Ａ／Ｄ，Ｄ／Ａ转换器的设计韩淑清（电气工程系）关键词：模－数转换器；数－模转换器；微处理机；锁相环中图分类号：ＴＰ３３５在微机控制系统中常使用的传感器和被控装置多为模拟量的输出、输入形式，要求在传感器和微机之间将模拟量转换为数字量；在微机与被控...     

In-plane Auto-Parametric Vibration of Inclined Cables under Random Transverse Excitation

In-plane auto-parametric stochastic vibration of inclined cables subjected to Gaussian white noise in transverse bridge orientation is investigated. Based on Newton＇s laws of motion and Galerkin＇s modal truncation principle, the influences of geometry nonlinearity induced by sag and large displacement of cables and the initial equilibrium state are taken into account. Meanwhile, the three-dimensional non-linear differential equations of inclined cables for coupling vibration are deduced, equivalent stochastic linearization method is applied to derive the 14-dimensional first-order nonlinear differential equations of state vectors, and the Runge-Kutta integration method is utilized to obtain the root mean square （RMS） response. Results show that when the transverse random excitation imposed on the stayed cable exceeds a critical value, the in-plane transverse vibration of the cable are excited due to tim auto-parametric nonlinear coupling, and the critical value of random excitation increases with the damping ratio. In this motion, the cable response possesses non-stationary characteristics, even though the loading keeps stationary.     

多物理域耦合求解的轮毂电机温度场

为研究温度变化对电动汽车用轮毂电机的工作性能和使用寿命的影响，采用场路耦合法将轮毂电机有限元模型与外电路联合求解，建立了包含轮毂电机本体、外部驱动控制电路的联合仿真模型，充分考虑了外部激励中时间谐波电流对磁场的影响. 然后，将计算得到的绕组铜耗、定子铁芯损耗、永磁体涡流损耗以及杂散损耗等作为热源，采用磁热耦合法将其耦合到各部件进行瞬态温度场研究，综合考虑了电机工作过程中其损耗分布在时间和空间位置上的瞬态变化特性，热源损耗与温度场实时精确耦合. 详细研究了负载运行时轮毂电机各部件温度随时间的变化情况，以及温度的空间分布特性. 多物理域耦合法实现了电磁场与外电路的直接耦合，电磁场与温度场的顺序耦合. 最后，对轮毂电机进行台架试验. 研究结果表明:仿真计算结果与试验结果在额定工况下温度的最大误差为4.96%，峰值工况下最大误差为10.55%.      

10 kV交流XLPE电缆改为直流运行的热电耦合仿真

为了研究电缆在不同敷设方式和直流拓扑结构时的直流运行参数,以10?kV交流配电网中广泛使用的三芯交联聚乙烯(cross-linked?polyethylene,XLPE)电缆为例,通过有限元仿真软件建立电缆温度场、流场和电场耦合仿真模型,对直埋敷设、排管敷设和沟槽敷设下电缆分别以双极式、单极式、三线双极式(three-...     

基于小波变换的斜拉桥索双轴漏磁检测方法

针对在役斜拉桥索只能进行无损检测的特点,提出了基于漏磁检测的缆索缺陷探伤方法以及检测电路.由于检测现场空间磁场噪声较强,导致漏磁信号特征不明显,为此,应用二进小波变换的方法,对周向漏磁信号采用基于高斯白噪声的快速离散软阈值算法进行信噪分离,以确定缆索缺陷程度;对轴向漏磁检测信号进行奇异性检测处理,以获取缺陷的精确位置信息.实验结果表明,该方法可实时获取缆绳索缺陷程度和位置信息.     

Parametric vibration and vibration reduction of cables in cable-stayed space latticed structure

Mechanical model and vibration equation of a cable in cable-stayed sparse latticed structure (CSLS) under external axial excitation were founded. Determination of the mass lumps and natural frequencies supplied by the space latticed structure (SLS) was analyzed. Multiple scales method (MSM) was introduced to analyze the characteristics of cable's parametric vibration, and the precise time-integration method (PTIM) was used to solve vibration equation. The vibration behavior of a cable is closely relative to the frequency ratio of the cable and SLS. The cable's parametric vibration caused by the external axial excitation easily occurs if the frequency ratio of the cable and SLS is in a certain range, and the cable's vibration amplitude varies greatly even if the initial disturbance supplied by SLS changes a little. Furthermore, the mechanical model and vibration equation of the composite cable system consisting of main cables and assistant cables were studied. The parametric analysis such as the pre-tension level and arrangement of the assistant cables was carried out. Due to the assistant cables, the single-cable vibration mode can be transferred to the global vibration mode, and the stiffness and damping of the cable system are enhanced. The natural frequencies of the composite cable system with the curve line arrangement of assistant cables are higher than those with the straight-line arrangement and the former is more effective than the latter on the cable's vibration suppression.     

一种应用于电动汽车的新型耦合机构优化设计

针对电动汽车无线充电应用,提出了一种凹凸型磁耦合机构,在减小磁芯体积的情况下实现了更好的耦合特性,提高了系统功率传输能力. 基于有限元理论,利用COMSOL电磁场仿真软件,建立了凹凸型耦合机构的有限元仿真模型,针对线圈两端凸起磁芯高度、线圈两端凸起磁芯长度配比、磁芯长度、磁芯长度与宽度之间的约束关系以及磁芯厚度等主要结构参数从互感及耦合系数等角度分别进行了分析和优化设计,并讨论了磁芯变薄后的磁饱和特性. 通过仿真和实验测试结果验证了所设计耦合机构的可行性及在磁场分布及耦合特性方面的优势,使得系统的输出功率和效率相对原条状磁芯结构分别提高了37%和10%.      

三塔斜拉桥多点激励地震反应特性分析

以某空间框架式索塔3塔连续梁支承体系斜拉桥为例,采用多点时程反应分析方法研究了纵向和横向多点激励（仅考虑行波效应）对该类型桥梁地震响应的影响。研究结果表明：纵向多点地震激励下,行波效应对3塔斜拉桥中塔受力影响较小,边塔较大;同样,行波效应对两中跨主梁影响相对较小,两边跨则较大。横向多点地震激励下,无论是对于3塔斜拉桥中塔还是边塔,行波效应对于主塔受力是有利的,随着行波波速的降低,主塔响应呈下降趋势,对主梁来说,则可能放大主梁地震响应;存在一个最不利行波波速,在该行波波速下,结构响应取最大值。     

Design of Braunbeck Coil for Nuclear Magnetic Resonance Gyro Magnetic Field Excitation

For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro (NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. This study introduces Braunbeck coil that can be used in magnetic field excitation system. Braunbeck coil can produce homogeneous magnetic field within a limit space, and occupy a small volume. In addition, this study presents mathematical expressions that can be used to calculate the area of uniform magnetic field. Experimental test verifies the effectiveness of the proposed design, and the results accord closely with the actual simulation.     

Magnetic field tuning characteristics of bimodal ultrasonic motor stator

The magnetic field tuning characteristics of an ultrasonic motor (USM) stator are discussed. The stator consists of two piezoelectric ceramic transducer (PZT) plates and one sandwiched-in Terfenol-D plate. The dimensions of the stator are carefully adjusted to specifically discuss the influence of the magnetic field on the frequency difference between the longitudinal and bending modes of the stator. The frequency difference discussed in this paper is usually small and mainly caused by uneven materials, machining errors and changes in external conditions (temperature, pre-stress or load). The longitudinal and bending modes of the stator are simultaneously excited by an external electric field to generate the elliptic motion trajectories of the driving points. A direct current (DC) magnetic field is applied to decrease the difference between the two mode frequencies of the fabricated stator. In experiments, the dependences of the two mode frequencies and their difference on DC magnetic fields are all investigated. The experimental results indicate that the difference between the longitudinal and bending mode frequencies of the PZT/Terfenol-D/PZT composite stator can be tuned by changing the intensity of the external DC magnetic field.     

可重构斜拉索磁性无损检测机器人技术研究

针对斜拉索的特征,提出一种在役斜拉索检测机器人技术方案.采用模块化可重构磁性检测技术,利用磁性检测系统励磁场产生的磁场力作为机器人沿斜拉索爬升所需的附着力,使单元模块同时具有检测及爬升功能.根据不同的拉索直径,选用不同数量的模块进行重构形成对应的自主爬升检测机器人.理论分析及试验研究表明,该可重构斜拉索磁性检测机器人可对不同直径、任意倾斜角的斜拉索进行无损检测,具有体积小、重量轻、安全可靠等特点,有良好的应用前景.