Zn掺杂对Bi2212单晶临界电流密度的影响

通过对少量Zn掺杂Bi2212单晶样品不同温度下的磁滞回线的测量,根据Bean临界态模型得到了样品在不同温度和磁场下的临界电流密度.发现不同温度下的临界电流密度与磁场的关系可以用Jc(H,T)=Jc(0,T)exp(-Hα)进行拟合,并且拟合参量α随温度的上升而增大,而在Pb掺杂和纯Bi2212单晶中α值基本上是不随温度变化的.将得到的Jc与Pb掺杂和纯Bi2212单晶的结果进行比较,发现在相同的温度和磁场下Zn掺杂样品具有最高的临界电流密度,表明少量Zn掺杂使得样品的临界电流密度得到提高.Zn掺杂对Bi2212体系临界电流密度的提高主要来源于在材料中引入了有效的涡旋钉扎中心,而Pb掺杂体系中Jc的提高是体系的层间耦合增强导致的结果.     

MgxB2起始成分对不可逆场和临界电流密度的影响

我们用固相反应法成功合成了MgrB2（0．5≤x≤1．3）系列样品，并对其结构，临界电流密度（Jc）和不可逆场（Hirr）进行了研究．实验结果表明，随着x增大晶格常数α逐渐增大，而晶格常数c在x=0．9左右达到最大值．所有x〉0．5的样品在零场下的Jc值都在10^6A／cm^2左右．然而在高磁场下，Mg缺位的样品的Jc值要比Mg富足的样品的Jc值大．20K时．Mg0．8B2样品的不可逆场达到最大值5．2T，比MgB2样品要高出0．8T．研究表明，高磁场下Hirr和Jc的增大可能与MgB4纳米粒子的形成有关．     

外应力场下双层铁磁薄膜中的铁磁共振性质

用铁磁共振方法得到了双层铁磁薄膜的色散关系解析表达式.发现共振场依赖于层间耦合强度和应力场.假定层间为反铁磁性耦合，且铁磁层Ａ有较强的平面内各向异性.随着外磁场的增强，铁磁层Ｂ中的磁化强度突然由最初的反平行转为平行，从而导致色散曲线的阶跃，并且发现光学模阶跃幅度比声学模大.随着应力场的增强，Ｂ层中磁化强度反转所需的外磁场减弱.此外，在不同的交换耦合强度和应力场下，光学模共振场对外磁场方向的依赖性较强. 关键词： 双层铁磁薄膜 界面相互作用 应力各向异性场 铁磁共振     

两层星形网络的特征值谱及同步能力

多层网络是当今网络科学研究的一个前沿方向.本文深入研究了两层星形网络的特征值谱及其同步能力的问题.通过严格导出的两层星形网络特征值的解析表达式,分析了网络的同步能力与节点数、层间耦合强度和层内耦合强度的关系.当同步域无界时,网络的同步能力只与叶子节点之间的层间耦合强度和网络的层内耦合强度有关;当叶子节点之间的层间耦合强度比较弱时,同步能力仅依赖于叶子节点之间的层间耦合强度;而当层内耦合强度比较弱时,同步能力依赖于层内耦合强度;当同步域有界时,节点数、层间耦合强度和层内耦合强度对网络的同步能力都有影响.当叶子节点之间的层间耦合强度比较弱时,增大叶子节点之间的层间耦合强度会增强网络的同步能力,而节点数、中心节点之间的层间耦合强度和层内耦合强度的增大反而会减弱网络的同步能力;而当层内耦合强度比较弱时,增大层内耦合强度会增强网络的同步能力,而节点数、层间耦合强度的增大会减弱网络的同步能力.进一步,在层间和层内耦合强度都相同的基础上,讨论了如何改变耦合强度更有利于同步.最后,对两层BA无标度网络进行数值仿真,得到了与两层星形网络非常类似的结论.     

陶瓷超导体的磁化强度和临界电流密度

假定晶内临界电流密度 Jc 为常量(Bean 模型),由磁化强度定义直接计算了四种形状的晶粒的不可逆磁化强眨 M 与 Jc 的关系,得到了相应的 Jc(△M)中的几何因子修正量.对第二类超导体,退磁场和退磁因子在 Meissner 态和H_(c1)附近的混合态仍是重要的,在其余磁场中都可以忽略.对氧化物陶瓷超导块,由于弱连接,晶间磁场近似等于外场.讨论了块样中非超导部分对实验测量的磁化强度■及 Jc 估算的影响.     

MgB2／Fe带材Jc的各向异性及MgB2芯织构和成分不均一性的研究

本文研究了在不同磁场方向和温度下非原位Fe包套MgB2单芯带Jc的各向异性，通过对各种工艺条件下带材中MgB2芯的X-ray衍射图进行拟合分析和计算，比较了MgB2芯在Fe-MgB2界面和中心处的织构度和成份不均一性．研究发现带材Jc的各向异性受初始粉末颗粒尺寸的影响．由于受套管材料强度和形变加工工艺的影响，MgB2芯在Fe-MgB2界面处比在中心处有较强的织构．在MgB2-Fe的界面处，700℃淬火样品的X-ray衍射图中发现了由中间相Fe23B6生成的金属间化合物Fe2B另外还研究了MgB4和MgO等主要杂质相的形成原因．     

Bi系多芯丝超导带材的超导性能与微观组织分析

本文采用XRD和SEM技术分析了具有不同临界电流密度（Jc）的Bi系多芯超导带材．结果表明，样品中Bi-2223晶粒高度取向排列，其取向因子F值在0．947-0．977范围内．SEM分析结果发现，高Jc样品中在平行于带材平面的片状的Bi-2223晶粒的晶界处残留的杂质主要为CuO晶粒，它与Bi-2223晶体结合紧密．在低Jc的样品中，Bi-2223晶片边界存在的杂质颗粒尺寸较大，其成分为（St，Ca）CuO和CuO的混合体．样品的横断面和纵断面的SEM观察发现，在高性能的样品中，芯丝烧结体的致密度较高．枝条状Bi-2223晶体穿过银层，在芯丝之间形成了很强的连接体．本文讨论了临界电流密度与微观组织的关系．     

MGxB2起始成分对不可逆场和临界电流密度的影响

我们用固相反应法成功合成了MgxB2(0.5≤x≤1.3)系列样品,并对其结构,临界电流密度(Jc)和不可逆场(Hirr)进行了研究.实验结果表明,随着x增大晶格常数a逐渐增大,而晶格常数c在x=0.9左右达到最大值.所有x>0.5的样品在零场下的Jc值都在106A/cm2左右.然而在高磁场下,Mg缺位的样品的Jc值要比Mg富足的样品的Jc值大.20K时,Mg0.8B2样品的不可逆场达到最大值5.2T,比MgB2样品要高出0.8T.研究表明,高磁场下Hirr和Jc的增大可能与MgB4纳米粒子的形成有关.     

S/S′层状超导体的穿透深度

在Ｓ／ Ｓ′层状超导材料中,由于邻近效应的存在,其超导电性在垂直于层的平面方向是空间变化的．本文通过一个Ｓ／Ｓ′系统的邻近效应模型,其中Ｔｃ,Ｓ＞ Ｔｃ,Ｓ′,研究了磁场穿透深度λ（Ｔ） 在材料及样品参数变化时的特性．研究表明,随着Ｓ′层的厚度、超导转变温度、电阻率、以及Ｓ／Ｓ′的层间耦合强度的改变,λ（ Ｔ） 显示出丰富的特性,其中许多特征与近年来对常规超导系统及高Ｔｃ 超导材料中的测量所得的结果类似     

多层单向耦合星形网络的特征值谱及同步能力分析

随着复杂网络同步的进一步发展,对复杂网络的研究重点由单层网络转向更加接近实际网络的多层有向网络.本文分别严格推导出三层、多层的单向耦合星形网络的特征值谱,并分析了耦合强度、节点数、层数对网络同步能力的影响,重点分析了层数和层间中心节点之间的耦合强度对多层单向耦合星形网络同步能力的影响,得出了层数对多层网络同步能力的影响至关重要.当同步域无界时,网络的同步能力与耦合强度、层数有关,同步能力随其增大而增强;当同步域有界时,对于叶子节点向中心节点耦合的多层星形网络,当层内耦合强度较弱时,层内耦合强度的增大会使同步能力增强,而层间叶子节点之间的耦合强度、层数的增大反而会使同步能力减弱;当层间中心节点之间的耦合强度较弱时,层间中心节点之间的耦合强度、层数的增大会使同步能力增强,层内耦合强度、层间叶子节点之间的耦合强度的增大反而会使同步能力减弱.对于中心节点向叶子节点耦合的多层星形网络,层间叶子节点之间的耦合强度、层数的增大会使同步能力增强,层内耦合强度、节点数、层间中心节点之间的耦合强度的增大反而会使同步能力减弱.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.