Seismic base isolation by nonlinear mode localization

Summary In this paper, the performance of a nonlinear base-isolation system, comprised of a nonlinearly sprung subfoundation tuned in a 1∶1 internal resonance to a flexible mode of the linear primary structure to be isolated, is examined. The application of nonlinear localization to seismic isolation distinguishes this study from other base-isolation studies in the literature. Under the condition of third-order smooth stiffness nonlinearity, it is shown that a localized nonlinear normal mode (NNM) is induced in the system, which confines energy to the subfoundation and away from the primary or main structure. This is followed by a numerical analysis wherein the smooth nonlinearity is replaced by clearance nonlinearity, and the system is excited by ground motions representing near-field seismic events. The performance of the nonlinear system is compared with that of the corresponding linear system through simulation, and the sensitivity of the isolation system to several design parameters is analyzed. These simulations confirm the existence of the localized NNM, and show that the introduction of simple clearance nonlinearity significantly reduces the seismic energy transmitted to the main structure, resulting in significant attenuation in the response. This work was supported in part by the National Science Foundation Grant CMS 00-00060. The authors are grateful for this support.     

晶体管发射极电流集边效应物理意义之探讨

由基区电阻的自偏压引起的晶体管发射极电流集边效应，是限制晶体管承载电流能力的因素之一。     

音响用低压大电流器件功率容量研究

本文介绍了一种提高晶体管二次击穿耐量的方法，并从理论上作了探讨。     

一种GSM基站中的串话检测方案

串话现象是移动通信中较常见的故障现象之一。本文就串话现象及其原因进行分析,提出在基站子系统传输的语音帧中加入测试比特位的方案,根据测试前后测试比特位的比较,达到检测基站是否产生串话现象的目的。     

Calcium Bis[bis(trimethylsilyl)amino‐triethylgallate] — A Molecule with Ca‐C‐Ga Three‐Center Bonds

The reaction of calcium‐bis[bis(trimethylsilyl)amide] with two equivalents triethylgallium yields nearly quantitatively the addition product. In the solid state the calcium atoms are coordinated by two nitrogen atoms and two ethyl groups, whereas in solution all ethyl substituents are magnetically equivalent even at low temperatures. The Ca‐C‐Ga two‐electron three‐center bonds show mean Ca‐N and Ca‐C distances of 243 and 268 pm, respectively.     

GSM无线网络容量规划方法新探

首先论述了无线网有效话务量与无线网理论处理能力的关系，得出了无线网络利用率的理想取值范围，然后提出了引入无线网络利用率的概念和计算GSM网基站配置的方法；最后提出了提高无线网络资源利用率的有效措施。     

Personal Trusted Devices for Web Services: Revisiting Multilevel Security

In this paper we revisit the concept of mandatory access control and investigate its potential with personal digital assistants (PDA). Only if applications are clearly separated and Trojans cannot leak personal information can these PDAs become personal trusted devices. Limited processing power and memory can be overcome by using Web services instead of full-fledged applications – a trend also in non-mobile computing. Web services, however, introduce additional security risks, some of them specific for mobile users. We propose an identification scheme that can be effectively used to protect privacy and show how this system builds upon a light-weight version of mandatory access control.     

埋入无源元件集成的高密度印制板

概述了Motorola的埋入PTF电阻、CFP电容和螺旋电感等无源集成的高密度印制板和埋入无源集成技术。     

多芯片组件热阻技术研究

在传统单芯片封装热阻定义的基础上,针对多芯片组件(MCM)传统热阻表示方法的不足,基于线性叠加原理,采用有限元模拟技术,提出了MCM的结到壳的热阻表示方法——热阻矩阵,并利用有限元模拟方法对热阻矩阵进行了验证。结果表明,采用热阻矩阵方法预测器件结温的误差小于2%。     

流量经营时代的大数据处理技术应用研究

移动互联网的快速发展及流量收入占比的快速攀升,促使流量经营成为运营商战略转型的重点。运营商传统数据存储与处理技术无论是从成本、性能还是扩展性等方面都受到了巨大挑战。探讨了流量经营时代运营商引入大数据处理技术的必要性与具体实施方案,并通过实践验证大数据技术带来的效益,以此指导运营商实施大数据解决方案。