沟道应力对GaAs PHEMT材料电性能的影响

设计并用分子束外延(MBE)法制备了不同沟道结构的GaAs PHEMT材料,采用高分辨率X射线双晶衍射仪(DCXRD)、应力测试仪和霍尔测试仪对样品的结晶质量、薄层组分和厚度偏差、应力以及电子迁移率进行了分析表征。探讨了外延片应力与沟道结构的相关性,研究了沟道失配应力对电性能的影响机理。建立了GaAs PHEMT材料热应力引起电子传输特性退化的试验方法,进行了高温和低温存储后材料电性能的演化行为测试,并归纳了热应力引起材料电特性退化的实验结果。结果表明GaAs PHEMT材料经高、低温存储并恢复室温后仍能保持原有电性能,沟道应力对材料电性能的影响主要表现为失配应力。     

FIR滤波器在扩频发射机中的应用

直接序列扩频技术以保密性强和抗多径衰落等优点而获得广泛的应用,针对在多系统兼容工作时出现的邻近通道干扰的问题,从扩频通信的工作原理入手进行分析,分析邻近通道干扰产生的来源,采用基带信号有限脉冲响应(FIR)滤波器的方式,实现邻近通道抑制的要求。在此基础上设计的解决方案,经过实际系统试验验证,可以很好地解决邻近通道干扰的问题。     

泊松比取值对InGaAs/GaAs异质结组分分析的影响

通过对InxGa1-xAs泊松比的两级优化,讨论了泊松比取值对InxGa1-xAs/GaAs异质结应变层中组分分析的影响.以PB模型计算的临界厚度为指导,设计了一组实验,采用分子束外延(MBE)技术生长不同In组分、不同应变层厚度的InxGa1-xAs/GaAs异质结样品且进行X射线双晶衍射测试,并依据该结果分析应变层组分.对于影响组分分析的泊松比,通过线性内插法将应变层泊松比优化为组分的函数,并分别采用传统的单一值和优化的泊松比分析应变层的组分:泊松比取单一值1/3时,组分偏差高达0.009 1,取优化的泊松比时,偏差仅0.001 5.研究表明,相对于取单一值和线性内插法优化的泊松比,采用线性内插弹性系数优化的泊松比可以更准确地分析异质结应变层的组分.     

A density-wave-like transition in the polycrystalline V3Sb2 sample with bilayer kagome lattice

Recently,transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena.Here we report on the synthesis,structure,and physical properties of a bilayer kagome lattice compound V₃Sb₂.The polycrystalline V₃Sb₂ samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850℃.Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at Tdw≈160 K with a large thermal hysteresis,even though some sample-dependent behaviors were observed presumably due to the different preparation conditions.Upon cooling through Tdw,no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements.This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa,around which no sign of superconductivity was observed down to 1.5 K.Specific-heat measurements revealed a relatively large Sommerfeld coefficientγ=18.5 mJ·mol^-1·K^-2,confirming the metallic ground state with moderate electronic correlations.Density functional theory calculations indicate that V₃Sb₂ shows a non-trivial topological crystalline property.Thus,our study makes V₃Sb₂ a new candidate of metallic kagome compound to study the interplay between density-wave-order,nontrivial band topology,and possible superconductivity.     

融合时域像特征的空间可见光小目标检测技术

在对空间目标进行远距离可见光成像观测过程中,由于目标信号较弱而且平台不稳,目标的信号因在焦平面上产生亚像素抖动而大大削弱,增加了远距离目标检测的难度。针对远距离目标检测难题,提出一种融合像素点时域像均值与方差两种特征的远距离弱信号目标检测算法。经实测图像序列分析,存在弱目标的像素点与纯背景像素点相比,时域像方差因平台抖动而较大,利用这一特征结合广义似然比准则可以有效检测出图像中的弱目标。最后通过计算机仿真验证了检测算法的有效性。     

高电阻温度系数(La0.67Ca0.33MnO3)1-x∶Agx多晶陶瓷的研究

采用溶胶-凝胶法制备了(La0.67Ca0.33 MnO3)1-x∶Agx(x=0.00、0.10、0.15、0.20、0.3、0.4、0.5)系列多晶陶瓷样品,通过XRD、SEM和标准四探针法对材料晶体结构、表面形貌和电学性能的分析研究Ag的添加对材料性能的影响.结果表明:随着Ag添加量的增加,样品的晶格常数逐渐增大,这是由于Ag取代La3+、Ca2+进入晶格使其发生膨胀;并且样品的金属-绝缘体转变温度(Tp)随Ag添加量的增加而升高,从270 K(x=0)升高到281 K(x=0.5),这是由于Ag对La3+、Ca2+的替换导致Mn4+/Mn3+比例增大而提高了双交换作用.值得注意的是,当0.00≤x≤0.15时,TCR值随x的增大而增大,当x=0.15时达到最大值58.6;·K-1;0.15≤x≤0.5时,TCR反而随之降低,这可能是由于高添加量导致材料的烧结质量降低.     

van der Waals气体状态方程对于实际气体pV_m-p曲线的解释

为加深对物理化学中实际气体行为的认识,通过van der Waals方程对不同温度下实际气体的pV_m-p曲线进行了解释。     

高电阻温度系数的La0.67(Ca0.33-xSrx)MnO3多晶陶瓷制备与电学性能研究

采用溶-凝胶法在1450 ℃烧结12 h的条件下,制备了x组分为0、0.01、0.03、0.05、0.06、0.07的La0.67(Ca0.33-xSrx)MnO3 (LCSMO)多晶陶瓷,通过R-T、XRD和SEM测试分析,结果表明,溶胶-凝胶方法制备的LCSMO多晶陶瓷其物相较纯,阻温特性良好,晶粒尺寸大,致密度高.在未掺Sr时,该体系电阻温度系数(TCR)达到最高值42.5;.随着Sr掺杂比增加,金属-绝缘体转变温度TP升高,TCR降低,而在TP达到室温时,LCSMO多晶陶瓷具有较大的TCR(9;以上).在LCSMO多晶体系中如此大的TCR较为罕见,使其具有重要的潜在应用价值.     

High pressure synthesis and characterization of the pyrochlore Dy_2Pt_2O_7:A new spin ice material

The cubic pyrochlore Dy2Pt2O7 was synthesized under 4 GPa and 1000℃ and its magnetic and thermodynamic properties were characterized by DC and AC magnetic susceptibility and specific heat down to 0.1 K.We found that Dy2Pt2O7 does not form long-range magnetic order,but displays characteristics of canonical spin ice such as Dy2Pt2O7,including(1)a large effective moment 9.64μB close to the theoretical value and a small positive Curie-Weiss temperatureθCW=+0.77 K signaling a dominant ferromagnetic interaction among the Ising spins;(2)a saturation moment ~4.5μB being half of the total moment due to the local<111>Ising anisotropy;(3)thermally activated spin relaxation behaviors in the low(~1 K)and high(~20 K)temperature regions with different energy barriers and characteristic relaxation time;and most importantly,(4)the presence of a residual entropy close to Pauling’s estimation for water ice.     

基于PSCAD的无源滤波器仿真与应用分析

该文首先介绍了电力系统中三种常用无源滤波器的工作原理,然后利用电磁暂态仿真软件PSCAD/EMTDC搭建了这三种无源滤波器模型并分别进行了仿真,最后对仿真结果进行了对比分析,得出这三种无源滤波器在滤波性能和特征谐波阻抗方面的优缺点。此研究对钢铁公司变压器二次侧的谐波抑制和无功补偿的参数设计具有一定参考价值。