W波段回旋行波管输入输出段的改进设计

在回旋行波放大器的设计中,输入输出段的性能直接影响到整管输出功率、效率及增益。设计了一种采用渐变过渡段的输入耦合器来减少电子注在前端的截获,而且略微地提高了耦合特性,有效带宽达到4.06 GHz。采用二级切比雪夫渐变波导作为输出结构的耦合输出段,从仿真结果得到,在整个工作频段内,该结构中TE01工作模式的反射低于-20 dB,TE01模向杂模TE02和TE03的耦合分别在-20 dB和-30 dB以下。     

Oscillation of coercivity between positive and negative in MnxGe1-x：H ferromagnetic semiconductor films

Amorphous MnxGe1-x :H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron cosputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1-x :H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1-x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6 :H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1-x films for the application in spintronics.     

Co100-xMnx合金在GaAs(001)表面的生长结构和磁性的实验研究

对Co_100-xMn_x合金在GaAs(001)表面的分子束外延生长、晶体结构和磁学性质进行了研究.结果表明,当0100-xMn_x合金薄膜是体材料中不存在的体心立方(bcc)结构,并且具有较强的铁磁性,当44100-xMn_x合金薄膜最初为bcc结构,随着厚度的增加,逐渐从bcc向面心立方(fcc)结构转化,最后成为完全的fcc结构,薄膜具有较 关键词：     

数学建模课程的教学与综合素质教育

本文结合教学模型课的教学和竞赛的体会,探讨了综合性大学对大学生综合素质培养的思路和方法。认为教改的目的在于解决“面向”、“需求”和“服务”的问题。综合素质是评价教改的准则,课程建设是综合素质教育的核心和动力,教学内容、教学方法、教学手段的更新及参加竞赛是素质培养教育的良好途径和重要环节。     

圆筒试验JWL状态方程参数的贝叶斯标定

在研究数值模拟的输入参数引入的不确定性时,通常需要人为给定每个输入参数的概率分布,且输入参数概率分布的选择可能会对分析结果产生直接影响。利用贝叶斯方法标定了圆筒试验JWL状态方程参数,得到了标定参数的估计值和后验分布,并研究了不同统计模型假设对标定参数的估计值和后验分布的影响。贝叶斯后验分布融合了基准试验的试验数据的信息,因此将其作为不确定度量化分析时输入参数的初始概率分布,可以尽量减少分布选择引入的认知不确定性。     

Structural and physical properties of BiFeO3 thin films epitaxially grown on SrTiO3（001） and polar（111） surfaces

The influence of surface polarity on the structural properties of BiFeO3 （BFO） thin films is investigated. BFO thin films are epitaxially grown on SrTiO3 （STO） （100） and polar （111） surfaces by oxygen plasma-assisted molecular beam epitaxy. It is shown that the crystal structure, surface morphology, and defect states of BFO films grown on STO substrates with nonpolar （001） or polar （111） surfaces perform very differently. BFO/STO （001）is a fully strained tetragonal phase with orientation relationship （001）[100]BFOII（001）[100]STO, while BFO/STO （111） is a rhombohedral phase. BFO/STO （111） has rougher surface morphology and less defect states, which results in reduced leakage current and lower dielectric loss. Moreover, BFO films on both STO （001） and STO （111） are direct band oxides with similar band gaps of 2.65 eV and 2.67 eV, respectively.     

Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the `hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.     

辉光放电质谱法测定高纯材料中痕量硫杂质

准确测定并控制材料中杂质元素含量是发挥高纯材料性能不可或缺的环节。辉光放电质谱法(GDMS)是准确、快速、高灵敏分析高纯材料中痕量及超痕量硫的理想方法。对GDMS分析高纯铜和镍基高温合金中痕量硫的质谱干扰进行了讨论,优化了放电电流和放电电压,采用多种标准物质对硫的相对灵敏度因子(RSF)进行了校准和验证,并与二次离子质谱法(SIMS)进行分析结果比对,验证了GDMS定量分析结果的准确性和可靠性。     

匹配干涉结构对远程光纤传感系统噪声的影响

研究了采用内调制相位产生载波（PGC）解调的匹配干涉型光纤传感系统中匹配干涉结构对传输光纤拾音噪声的影响。结果表明：当补偿干涉仪与传感部分相邻时,光学微分效应的作用可大幅度降低由传输光纤光路拾音引入的相位调制噪声;匹配光程差的增加不仅加剧了光频噪声向相位噪声的转换,同时也会影响相位调制噪声的转换幅度。通过设计合适的匹配光程差,并将补偿干涉仪进行有效屏蔽后与传感部分相邻放置,可以有效减小系统的相位噪声。研究成果为光纤传感远程传输系统的综合设计及噪声抑制技术提供了理论及实验基础,具有一定的参考意义。     

Enhanced Spin Injection into ZnO Semiconductor Measured by Magnetoresistance

We prepare 2× （NiFe/CoZnO）/ZnO/（CoZnO/Co）×2 spin valve structures used for spin injection by sputtering and photolithography. In the junctions, the free magnetic layer 2× （NiFe/CoZnO） and the fixed magnetic layer （CoZnO/Co） × 2 are used to realize the spin valve functions in the external switch magnetic field. Since the wide gap semiconductor ZnO layer is located between the two magnetic semiconductor layers CoZnO, the electrical ,spin injection from the magnetic semiconductor CoZnO into the non-magnetic semiconductor ZnO is realized. Based on the measured magnetoresistance and the Schmidt model, the spin polarization ratio in the ZnO semiconductor is deduced to be 11.7% at 90K and 7.0% at room temperature, respectively.