Hopf Bifurcation Control of a Hyperchaotic Circuit System

This paper is concerned with the Hopf bifurcation control of a new hyperchaotic circuit system. The stability of the hyperchaotie circuit system depends on a selected control parameter is studied, and the critical value of the system parameter at which Hopf bifurcation occurs is investigated. Theoretical analysis give the stability of the Hopf bifurcation. In particular, washout filter aided feedback controllers are designed for delaying the bifurcation point and ensuring the stability of the bifurcated limit cycles. An important feature of the control laws is that they do not result in any change in the set of equilibria. Computer simulation results are presented to confirm the analytical predictions.     

基于异构双核的磁共振接收机的设计

提出了基于异构双核的低场核磁共振（Low-field Nuclear Magnetic Resonance,low-field NMR）接收机的设计,具有ARM（Adanced RISC Machines）和现场可编程门阵列（Field Programmable Gate Array,FPGA）先进的异构双核结构、高速的模数转换器（Analog to Digital Converter,ADC）采集、增益的可控以及可视化显示等特性,提高了整个系统的性能指标.设计中采用Xilinx公司的系统开发工具System Generator来实现内部信号处理功能.实验结果表明,数字接收机具有结构紧凑、可重构性强、采样速率高和成本低等特点,并且增益的可控使接收机获得了较大的动态范围,提高了重建图像的信噪比（Signal-to-Noise Ratio,SNR）.     

硫酸镁微液滴水和重水交换动力学的微区拉曼研究

本文利用微区拉曼技术,研究硫酸镁液滴水和重水交换的动力学.在低湿度时,由接触离子对连接形成的链状结构使硫酸镁液滴表面形成胶态结构,阻碍其与环境之间的水交换,造成表面和内部的结构差异.拉曼光谱的高空间分辨能力为观测这一特殊的表面结构提供了便利.沉积在聚四氟乙烯疏水基底上的硫酸镁重水液滴呈球形,可以实现对液滴表面和中心的两...     

激光激发水中产生超声波的实验研究

采用压电陶瓷水听器研究了Nd：YAG脉冲激光激发水中产生瞬态超声波的特性,给出了声压信号随距离的变化关系。研究结果表明：用激光产生水下声波是完全可行的。当观测点与光击穿区的距离r远大于柱体长度时,垂直于光传播方向的激光瞬态超声波幅值与r成反比;当观测点与光击穿区的距离r很小时,垂直于光传播方向的声压幅值与产成反比。此外,当激光入射角度发生变化,超声脉冲的幅值也随之发生变化,其幅值在激光束垂直入射的时候最大。     

提高近红外光谱法检测人体血液等复杂溶液成分准确度的研究进展

近红外光谱常被用于含氢有机物质等的物化参数测量,可以提供丰富的结构和组成信息在复杂溶液的光谱定量分析中更是被广泛应用.然而在人体血液等复杂溶液的近红外光谱分析中,强大的背景信息造成的噪声干扰和冗余变量的存在,严重影响着样品的光谱测量和分析,影响着分析的效率和准确度.如何消除背景噪声等的干扰来提高分析准确度已经引起高度重...     

流动注射-化学发光法定量测定同一水域中的腐殖酸

采用流动注射-化学发光(FI-CL)这一灵敏的检测方法,通过条件实验与参数优化,优选了测定环境中痕量多羟基酚类化合物的发光体系,通过考察天然水体中的腐殖酸对化学发光-多羟基酚测定体系的影响,为来自于水及土壤中的实际样品中腐殖酸的检测提供了参考,建立了同一区域水体中腐殖酸的化学发光定量测定方法。 所得线性回归方程y=70.36x+540.1,相关系数r=0.995 4,线性范围为3～15 mg·L-1,检测限为0.749 mg·L-1,HA浓度为6 mg·L-1时的相对标准偏差(RSD)为1.08%。     

金纳米颗粒的有序制备及其光学特性

采用纳米球蚀刻技术在石英衬底上制备了不同高度的金纳米颗粒阵列.通过扫描电子显微镜对其表面形貌进行了观测,表明金纳米颗粒为有序分布的三棱柱结构.通过红外—紫外吸收光谱仪在190—900nm波长范围内对其光吸收特性进行了测量, 并成功观测到了金纳米颗粒表面等离子体振荡效应引起的光吸收峰,结果表明随着金纳米颗粒高度的增加,其吸收峰的位置向短波方向移动(蓝移).同时对金纳米颗粒的光吸收特性进行了基于离散偶极子近似的理论计算,并与实验结果进行了比较. 关键词： 纳米球蚀刻技术 金纳米颗粒 离散偶极子近似     

电子元件的老化与筛选

为了保证电子元件使用的可靠性和稳定性,需要进行老化与筛选.电子元件的失效分为早期失效、正常使用期和损耗老化失效期三个阶段.除了常用的老化筛选方法之外,还可采用自然老化和简易老化方式.以场效应管功率老化系统为例研究了常用试验装置.国产电子元件需加强老化筛选这个环节.     

MgO(001) barrier based magnetic tunnel junctions and their device applications

Spintronics has received a great attention and significant interest within the past decades,and provided considerable and remarked applications in industry and electronic information etc.In spintronics,the MgO based magnetic tunnel junction(MTJ) is an important research advancement because of its physical properties and excellent performance,such as the high TMR ratio in MgO based MTJs.We present an overview of more than a decade development in MgO based MTJs.The review contains three main sections.(1) Research of several types of MgO based MTJs,including single-crystal MgO barrier based-MTJs,double barrier MTJs,MgO based MTJs with interlayer,novel electrode material MTJs based on MgO,novel barrier based MTJs,novel barrier MTJs based on MgO,and perpendicular MTJs.(2) Some typical physical effects in MgO based MTJs,which include six observed physical effects in MgO based MTJs,namely spin transfer torque(STT) effect,Coulomb blockade magnetoresistance(CBMR) effect,oscillatory magnetoresistance,quantum-well resonance tunneling effect,electric field assisted magnetization switching effect,and spincaloric effect.(3) In the last section,a brief introduction of some important device applications of MgO based MTJs,such as GMR & TMR read heads and magneto-sensitive sensors,both field and current switching MRAM,spin nano oscillators,and spin logic devices,have been provided.