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脉冲激光探测电路的设计是激光应用领域的重要内容,根据脉冲激光信号的特点,从探测能力、响应时间、稳定性三方面对脉冲激光探测电路的设计进行研究,重点论述了光电探测系统组成的三个重要组成部分:光电探测器、光电转换电路和探测器偏置电路。深入分析了光电探测器的选型、利用电阻进行光电转换电路的特性以及利用跨导放大器进行光电转换电路的特性,对于激光探测系统的设计有一定参考价值。 相似文献
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氮化铝轮廓模式谐振器(CMR)能够满足现代无线通信对单片、多频段、可重构的多频率源的需求,具有很大的应用前景。针对目前无具体单个CMR频点的设计方法,提出了一种结合CMR性能参数的影响因素分析和有限元计算的CMR设计方法。该文对CMR的谐振频率、质量因子、机电耦合系数和动态电阻等谐振器主要性能参数的影响因素进行理论分析得到CMR结构的初始尺寸,再利用COMSOL有限元软件建立CMR几何模型并进行频域求解得到相应的频率-导纳曲线和频率-质量因子曲线;根据仿真结果和理论计算对CMR初始结构尺寸进行优化,并仿真设计了一个氮化铝CMR,其谐振频率为300 MHz,质量因子约为1 010,机电耦合系数约为1.64%。 相似文献
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采用脉冲激光溅射沉积技术在LaAlO3(001)衬底上制备了一系列不同厚度(40~240 nm)的La0.67Ba0.33MnO3薄膜。通过控制薄膜的厚度,获得了不同应变态的La0.67Ba0.33MnO3薄膜。根据X射线衍射(XRD)数据详细分析了薄膜厚度变化对c轴晶格常数的影响。采用标准的直流四探针法和超导量子干涉仪分别测量了薄膜的电阻温度特性和磁化强度温度特性。研究发现,La0.67Ba0.33MnO3薄膜的居里温度和金属绝缘态转变温度随压缩应变的增大而减小,即压缩应变抑制了La0.67Ba0.33MnO3薄膜的铁磁性,降低了居里温度。这一结果与以往压缩应变增强铁磁性并提高居里温度的结论相异,不能利用Millis的应变理论模型进行定性解释。利用超巨磁电阻(CMR)薄膜材料的应变效应对eg轨道稳定性的影响对La0.67Ba0.33MnO3薄膜的异常磁电输运效应进行了解释。 相似文献
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由于稀土合金锰氧化物在电子输运和自旋磁性等方面具有优异特性,人们对其潜在的应用寄予了很高的期望.近5年来,人们发展了一种新型的p-n结结构:在n型掺杂的SrTiO3单晶衬底上生长具有p型性质的钙钛矿锰氧化物薄膜,制成p-n异质结结构.本文重点介绍这种新型p-n异质结的研究进展,并对该类p-n异质结的应用前景进行展望. 相似文献
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Concomitant with the development of metal-based spintronics in the late 1980s and 1990s, important advances were made on the growth of high-quality oxide thin films and heterostructures. While this was at first motivated by the discovery of high-temperature superconductivity in perovskite Cu oxides, this technological breakthrough was soon applied to other transition-metal oxides and, notably, mixed-valence manganites. The discovery of colossal magnetoresistance in manganite films triggered intense research activity on these materials, but the first notable impact of magnetic oxides in the field of spintronics was the use of such manganites as electrodes in magnetic tunnel junctions, yielding tunnel magnetoresistance ratios that are one order of magnitude larger than what had been obtained with transition-metal electrodes. Since then, research on oxide spintronics has been intense, with the latest developments focused on diluted magnetic oxides and, more recently, on multiferroics. In this paper, the most important results on oxide spintronics was reviewed, emphasizing materials physics as well as spin-dependent transport phenomena, and finally give some perspectives on how the flurry of new magnetic oxides could be useful for next-generation spintronics devices 相似文献
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Magnetic domain structure in manganites was investigated by Lorentz electron microscopy, in order to understand some unusual physical properties, such as a colossal magnetoresistance (CMR) effect and a metal-to-insulator (MI) transition. In particular, we examined the spatial distribution of the charge/orbital ordered (CO/OO) insulator state and the ferromagnetic (FM) metallic state in phase-separated manganites, (La5/8-xPrx)Ca3/8MnO3 for x = 0.375, by obtaining both the dark-field and Lorentz images. We found an unusual coexistence of the CO/OO and FM metallic states with micrometer size below a MI transition temperature of 60 K. Our experimental findings provide direct evidence of the phase separation found in CMR manganites. 相似文献
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对象关系模型和Bayes网络分别是关系理论和概率理论两个不同领域中最重要的模型,它们首次集成于本文引入的概率关系模型中,作为新型的概率模型,概率关系模型不仅继承了Bayes网络的大部分优点,而且关系特征和对象的概念使它能有效地克服Bayes网络在许多方面的不足,而成为对复杂系统模建的理想工具,是对Bayes网络的重要创新;作为新型的关系模型,概率关系模型也是对传统关系模型的重要创新,具备概率特征的对象关系模型有了处理不确定性问题的能力。概率关系模型的创建对复杂智能信息系统开发研究有有着特别重要的意义,本文首先评述Bayes网络和对象关系模型,然后在此基础上引入概率关系模型。 相似文献
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Hakan Johansson 《Circuits, Systems, and Signal Processing》2006,25(2):175-200
This paper introduces two classes of frequency-response masking
(FRM) linear-phase finite (length) impulse response (FIR)
filters for interpolation and decimation by arbitrary integer
factors M. As they are based on the FRM approach, the proposed
filters are low-complexity (efficient) sharp-transition
linear-phase FIR interpolation and decimation filters. Compared
to previously existing FRM linear-phase FIR filter classes for
interpolation and decimation, the new ones offer lower
complexity and more freedom in selecting the locations of the
passband and stopband edges. Furthermore, the proposed classes
of FRM filters can, as special cases, realize efficient
Mth-band FRM linear-phase FIR interpolation and decimation
filters for all values of M. Previously, only half-band
(M = 2) FRM linear-phase FIR filters have appeared in the
literature. The paper includes design techniques suitable for
the new filters and design examples illustrating their
efficiency. 相似文献
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Re:YAG-SiO2多组分玻璃光纤是以Re:YAG作为纤芯材料,以石英管作为包层材料,采用熔芯法利用拉丝塔在高温下拉制的特种光纤,具有掺杂浓度高、增益大、机械强度高、易与石英光纤熔接等优点,适用于短腔单频光纤激光器。文中介绍了Re:YAG-SiO2光纤的制备工艺,结合笔者课题组在该领域的研究工作,综述了近年来基于Re:YAG-SiO2光纤的单频激光技术在1.0 μm,1.5 μm及2.0 μm波段的研究进展,并对Re:YAG-SiO2光纤的制备及基于该类光纤单频激光器所存在的问题进行了归纳分析,对未来的发展进行了展望。 相似文献
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Marzetta T.L. Hochwald B.M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1999,45(1):139-157
We analyze a mobile wireless link comprising M transmitter and N receiver antennas operating in a Rayleigh flat-fading environment. The propagation coefficients between pairs of transmitter and receiver antennas are statistically independent and unknown; they remain constant for a coherence interval of T symbol periods, after which they change to new independent values which they maintain for another T symbol periods, and so on. Computing the link capacity, associated with channel coding over multiple fading intervals, requires an optimization over the joint density of T·M complex transmitted signals. We prove that there is no point in making the number of transmitter antennas greater than the length of the coherence interval: the capacity for M>T is equal to the capacity for M=T. Capacity is achieved when the T×M transmitted signal matrix is equal to the product of two statistically independent matrices: a T×T isotropically distributed unitary matrix times a certain T×M random matrix that is diagonal, real, and nonnegative. This result enables us to determine capacity for many interesting cases. We conclude that, for a fixed number of antennas, as the length of the coherence interval increases, the capacity approaches the capacity obtained as if the receiver knew the propagation coefficients 相似文献
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