磁通交流响应的锁模特性研究

本数值研究无序磁通点阵的交流响应．我们在交流驱动力叠加的速度-直流驱动力曲线上发现了锁模台阶．台阶宽度随交流驱动力振幅呈Bessel函数振荡．台阶速度线性依赖于交流驱动力频率．此外，我们还首次考察了温度对锁模特性的影响．发现：台阶速度不随温度的变化而改变，直至台阶消失；热涨落将抹平钉扎势，因此破坏微观速度的调制，另外热涨落还破坏磁通的相干运动，从而导致台阶宽度随温度呈指数衰减．     

双模非经典光场辐照下介观约瑟夫森结中超流的动力学行为

研究了直流偏置电压下介观约瑟夫森结在SU（1，1）双模相干态光场作用下超流的动力学行为、流压台阶和直流分量等特性．研究发现超流能够呈现明显的崩塌与复苏现象，对于经典电磁场和非耦合的双模相干态光场作用下的情况，超流不出现此现象，且其流压台阶结构与后两种情况也不相同． 关键词：     

T=0.72Tc全电流超导隧道结电子模拟器

本描述了电子模拟器模拟了工作温度Ｔ＝０．７２Ｔｃ时超导隧道电流，它不仅包含了频率，能隙以及非线性准粒子隧道电流中电阻和电抗项的作用，还考虑了非零温度的影响。给出了恒压源与恒流源偏置条件下的直流与交流Ｉ－Ｖ特性，还给出了上述两种偏置条件下约瑟夫孙台阶及光子辅助的准粒子台阶与外加交流电压及频率间关系。     

电磁发射用多级混合储能充电方式对比

从工作原理、器件参数指标、系统效率、纹波系数等方面深入研究对比了蓄电池到脉冲电容器的三种充电方式:直流斩波、恒压、台阶升压,并建立了仿真模型。理论推导与仿真结果显示台阶升压充电效率达到0.911,远高于恒压方式的0.5,其对于晶闸管等器件的参数指标要求却是直流斩波的1/n(n为电池组分组数),并且能在不增加开关损耗的基础上将纹波系数限制在16%,甚至更低。利用混合储能样机进行了台阶升压实验,所得数据与仿真波形吻合较好。结果表明,台阶升压方式最适合应用于混合储能。     

高Tc台阶结Josephson器件

采用预先在衬底上刻蚀出台阶然后原位外延生长高 T_c 超导薄膜的工艺,制备了高 T_c 台阶结 Josephson 器件.文中研究了直流 Josephson 电流对温度和外加微波功率的关系,实验结果与磁通流器件的行为基本相符.     

采用交流电阻法测量超导转变温度T_c——连续超导体出现多相转变台阶

本文介绍了一种高灵敏度的交流电阻法测量超导体转变温度T_c的实验装置,该装置使用交流调制讯号和锁相放大器.实验结果表明:使用该方法不仅能测量原来直流电阻法难以测量的截面较大的包铜钱材样品,而且能测出连续多相超导样品中的各相T_c.如原位法Nb_3Sn的T_c有三个转变台阶,青铜法稳定化Nb_3Sn有二个转变台阶,铅-铌并联模拟多相超导样品也有二个转变台阶。其转变曲线中各相转变台阶的幅值与各相的相对含量成一定的比例关系,曲线不是单调函数,在T_c前的曲线呈明显的负阻.用该方法测得的T_c值与直流电阻法和电感法所测得的T_c值完全一致.     

介观 Josephson 结与激发偶奇相干态的相互作用

本文研究介观 Josephson 结与激发偶奇相干态的相互作用。研究了存在非经典光场时介观 Josephson 结中超导电流的一些特性，诸如崩塌与复苏现象，流压台阶特性，直流分量涨落以及超导电流的量子相干等。结果显示，超导电流的涨落及期望值可呈现直流分量。结果还显示稳态超导电流量，超导电流涨落的直流分量以及超导电流直流分量的关联函数等皆与光场的相位有关。     

YBCO沟槽型台阶结和rf SQUID的制备及性能研究

本工作在沟槽型台阶衬底上用直流磁控溅射法外延生长ＹＢａ２Ｃｕ３Ｏ７－δ（ＹＢＣＯ）超导薄膜后,制备出台阶结和射频超导量子干涉器（ｒｆＳＱＵＩＤ）．液氮中器件的磁通灵敏度和磁场灵敏度分别达到２．０×１０－４Φ０／Ｈｚ和２９４ｆＴ／Ｈｚ．涂有真空导热硅脂作保护层的器件,至今寿命已达１０个月,经历了３０次以上（个别器件达５０次）测试过程中从液氮到室温的冷热循环,性能没有明显的变化,表现出很好的稳定性．通过研究,解决了制备ｒｆＳＱＵＩＤ器件工艺过程中存在的一些问题,提高了制备器件的可重复性,得到高性能器件的成品率达到３０％～５０％．     

高成品率台阶结DC—SQUIDs磁强计

我们在ＳＴＯ台阶基片上，采用脉冲激光沉积（ＰＬＤ）和直流磁控溅射法制备出ＹＢＣＯ外延超导薄膜，采用普通的光刻技术得到ＤＣＳＱＵＩＤ图形．器件的ＩＶ曲线具有ＲＳＪ模型描述的上翘特征；三角波调制幅度峰峰值大于４μＶ，磁场灵敏度优于１ｐＴ／Ｈｚ（白噪声区）；９个不同基片上的样品磁通锁定的成品率达到６７％．     

基于高温超导双晶结的约瑟夫森效应观测实验

基于YBa2Cu3O7-δ高温超导双晶结,组建了约瑟夫森效应测试装置.利用此装置观察了直流和交流约瑟夫森效应,并测量了约瑟夫森结的临界电流和夏皮罗台阶.     

Current-voltage characteristics of large Josephson tunnel junctions

An analytic expression of dc supercurrents through large Josephson tunnel junctions in the presence of both a dc voltage and a dc magnetic field is obtained. The magnetic field dependence of the calculated dc supercurrents is reasonably consistent with experiments.     

静电场作用下双势阱分子隧道效应的猝灭及能级裂距的非线性特性研究

讨论了在静电场作用下，双势阱分子中波函数随外加静电场定域的动态过程，以及能级裂距与外加静电场的关系.证明了静电场作用后，能级裂距既受隧道效应的影响，又受外加静电场的影响.所加静电场较小时与外场强度呈非线性关系，当外加静电场较大时，Stark效应对能级裂距的影响占了主导地位，使能级裂距随外加静电场线性地增大. 关键词： 双势阱 静电场 隧道效应 能级裂距     

Co-existence of multiple attractors in the PWM controlled DC drives

DC shunt and series drives are extensively used in the industry. The occurrence of bifurcation and chaos in dc shunt and permanent magnet drives are well known. It is observed that the behavior of the drives not only depends on the value of system parameters but also on the value of initial conditions. Multiple attractors can exist for same parameter value. Different choice of initial conditions gives different periodic behavior of the system. The drive is intended to operate in a parameter range to give period-1 behavior. We report the existence of sub- harmonic oscillations in the period-1 region of the bifurcation diagram along with co-existing attractor with fractal basin boundaries in PWM controlled dc series drives. The series drive is extensively used in electric traction and other applications. The dc drives are run with dc input voltage. This dc voltage may be derived from a dc source or an ac source with a rectifier. The dc series drive shows different bifurcation behavior when different types of input voltage and switching elements are used. The existence of period-1, period-2 and period-4 orbits are observed with different initial conditions in the desired period-1 region of the bifurcation diagram. The dependence of system’s behavior on initial condition may render the system’s behavior unpredictable. These phenomena may have serious implication in performance.     

Dependence of space charge field and gain coefficient on the applied electric field in photorefractive materials

Intensity dependent space charge field and gain coefficient in the photorefractive medium due to the two interfering beams have been calculated by solving the material rate equations in presence of externally applied dc electric field. The gain coefficient has been studied with respect to variations in the input intensity, modulation depth, concentration ratio and normalized diffusion field in the absence and presence of the externally applied dc electric field. Space charge field has also been computed by varying the intensity ratio in the presence and absence of the externally applied dc electric field. It has been found that the rate of change of the space charge field with the normalized dc field decreases with the increasing intensity ratio for different values of the normalized diffusion field. It has also been found that the externally applied dc electric field has appreciable effect only when it is larger than the diffusion field.     

Coaxial holographic data storage without recording the dc components

A technique of recovering the data pages from Fourier holograms recorded without the dc components is demonstrated theoretically and experimentally by use of a coaxial holographic storage system. A reconstructed image is obtained by adding a phase-modulated dc component of the signal beam on reading. The bit error rate of the reconstructed image is comparable with that for the hologram recorded with the dc component as well. Since high intensities of the dc components are not recorded in this technique, the dynamic range of the recording media can be saved, which potentially contributes to increasing the number of multiplexed holograms.     

Accurate control of a liquid-crystal display to produce a homogenized Fourier transform for holographic memories

We show an accurate procedure to obtain a Fourier transform (FT) with no dc term using a commercial twisted-nematic liquid-crystal display. We focus on the application to holographic storage of binary data pages, where a drastic decrease of the dc term in the FT is highly desirable. Two different codification schemes are considered: binary pi radians phase modulation and hybrid ternary modulation. Any deviation in the values of the amplitude and phase shift generates the appearance of a strong dc term. Experimental results confirm that the calculated configurations provide a FT with no dc term, thus showing the effectiveness of the proposal.     

Orientational photorefractive effects observed in poly(vinyl alcohol)/liquid crystal composites

60 ) as a photoconductive sensitizer under an applied dc field. Orientational photorefractivity was demonstrated by observing Raman–Nath diffraction beams with an external dc field. The photorefractive gratings were partially memorized even in the absence of the applied dc field. Received: 12 January 1998/Revised version: 2 February 1998     

Tunable Ba_0.5 Sr_0.5 TiO₃ film bulk acoustic resonators using SiO₂ /Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators(FBARs) based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3(BST) films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias(< 45 V) while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum(Mo) as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

铬-镧镀层的制备及其光谱性能

用电沉积法分别采用直流电源和脉冲电源制备铬-镧镀层(dc)和铬-镧镀层(pulse).分别用发射光谱法、X衍射法、能谱法和扣描电镜法等对镀层进行表征.铬-镧镀层(dc)为非晶态镀层,铬-镧镀层(pulse)中含有晶态的镧和碳化铬.铬-镧镀层(dc)和铬-镧镀层(pulse)的硬度分别为860.3和930.2 HV,比铬...     

喷射器扩压室结构设计优化研究

扩压室对喷射器内混合流体的降速增压有着重要影响.本文基于真实流体物性,采用气体动力学方法建立改进的一维混合模型并提出扩压室结构设计优化方法.将模型计算结果与文献实验值对比验证了模型的准确性.分析了扩压室结构参数与喷射器膨胀比、喷嘴喉部直径和混合室直径之间的关系.结果表明,扩压室半锥角α随膨胀比Pg/Pe、扩压室出口直径...