添加Nb对CaCu3Ti4O12陶瓷介电性能的影响

采用固相反应法制备了CaCu₃Ti_4-xNb_xO₁₂(x=0，0.01，0.04，0.08，0.2)陶瓷，样品在x取值范围内形成了连续固溶体.在40Hz—110MHz频率范围对样品进行了介电频谱分析，实验结果表明，与纯CaCu₃Ti₄O₁₂不同，含Nb试样除了在频率大于10kHz范围内出现的德拜弛豫 关键词： 巨介电常数 德拜弛豫 阻挡层电容 等效电路     

触发时序对直线型脉冲变压器输出参数的影响

 利用通用电路模型程序Pspice,建立了包含60级感应腔串联的单路直线型脉冲变压器（LTD）电路模型,次级传输线采用去离子水绝缘,计算分析了感应腔触发时序对LTD输出参数的影响。结果表明,控制触发时序能够显著改变LTD型驱动源的输出参数。当控制触发时序使得各级感应腔内的开关在闭合前承受一定过电压时,LTD输出电流比单级感应腔同等条件下的输出电流具有更短前沿和更高幅值。假定LTD开关过压击穿电压为400 kV,通过触发时序的优化可提高LTD装置输出性能：前沿从56.5 ns减少至12.5 ns,峰值从1 018 kA提高至1 340 kA。     

Plasma effect on the phase matching of high harmonic generation

By optimizing the phase matching condition of high harmonic generation(HHG) from a supersonic neon gas jet,the enhanced HHG in the region of 60-70 eV has been selected.Three-dimensional numerical calculation shows that plasma plays a significant role in the phase matching process of HHG in a supersonic gas jet with short medium length.Due to plasma formation,the harmonic emission decays as the laser intensity reaches over 3.5 × 10 14 W/cm 2.The plasma induces the broadening and blue shift of the HHG spectra,which provides a method for fine-tuning the harmonic wavelength.     

多重氢键自组装联萘酚和含氮化合物

作为相互识别的结果,(±)-2,2′-二羟基-1,1′-联萘酚可与4,4′,6,6′-四甲基-2,2′-联嘧啶、1,2-双(4-吡啶)乙烷、反式-1,2-双(4-吡啶)乙烯、4,4′-联吡啶-N,N′-双氧化物及双-2-吡啶基甲酮等多种含氮化合物分别形成外形良好的共晶化合物1,2,3,4及5.本文对5个共晶化合物的晶体...     

统计方法在研究微积分与后续课程相关性中的应用与实证分析

着眼于本科生后期专业课程的学习效果,探讨微积分课程学习效果的有效性.以北京理工大学某经管类专业全部学生大一大二两学年的学习成绩为依据,分析微积分课程学习与后续理科课程学习的相关性,提出评估微积分课程学习效果的量化指标θ值的概念,并基于回归分析和相关性分析给出其算法.在实例分析中,通过研究,发现学生微积分课程学习效果的好坏会影响他们对后续相关课程的学习,同时也发现学生将微积分知识运用到间接相关科目的能力比运用到直接相关的科目的能力薄弱.     

分子构型对有机半导体分子TPD,DDB和NPB激射性能的影响

N,N′-二苯基-N,N′-二（3-甲苯基）-1,1′-联苯-4,4′-二胺（TPD）分子已证明能够在掺杂和非掺杂平面波导结构中产生受激发射,然而对于该分子激射特性的机理却很模糊.为了得到其激射特性的微观解释,我们通过实验和量化理论研究TPD分子的吸收、光致发光、受激发射以及与TPD分子结构类似的两个分子：1,4-二（二苯胺基）联苯（DDB）和N,N′-二苯基-N,N′-二（1-萘基）-1,1′-联苯-4,4′-二胺（NPB）.我们发现,DDB分子具有与TPD分子相似的自发辐射放大（ASE）特性,然而NPB分子却没有ASE特性,尽管其斯托克斯位移较大,约0.754eV.量子化学计算分析中,我们利用密度泛函理论（DFT）和弗朗克-康登（Franck-Condon）原理研究分子在电子基态和激发态的分子构型以及电子基态的振动能级.理论分析表明,对于TPD和DDB分子,一些苯环中的较强高频拉伸模式（1199～1664cm-1）对PL谱中的第一振动带（0-1跃迁）有显著贡献,该振动带有利于形成激光的四能级系统.而对于NPB分子,相对大的萘基基团取代了TPD和DDB分子外围的甲基与苯环,会产生一些较强的分子低频振动模式（11～689cm-1）,这些低频振动模式则会破坏激光四能级系统.研究结果有助于深刻理解有机分子的激射特性,为新型激射材料的设计和应用提供了理论基础.     

Pressure-induced phase transition in transition metal trifluorides

As a fundamental thermodynamic variable, pressure can alter the bonding patterns and drive phase transitions leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient pressure. Using the swarm intelligence structural prediction method, the phase transition of TiF₃, from R—3c to the Pnma phase, was predicted at high pressure, accompanied by the destruction of TiF₆ octahedra and formation of TiF₈ square antiprismatic units. The Pnma phase of TiF₃, formed using the laser-heated diamond-anvil-cell technique was confirmed via high-pressure x-ray diffraction experiments. Furthermore, the in situ electrical measurements indicate that the newly found Pnma phase has a semiconducting character, which is also consistent with the electronic band structure calculations. Finally, it was shown that this pressure-induced phase transition is a general phenomenon in ScF₃, VF₃, CrF₃, and MnF₃, offering valuable insights into the high-pressure phases of transition metal trifluorides.     

直流叠加脉冲电压下FLTD气体开关击穿特性

分析了直流叠加脉冲电压(定义为复合电压)下次级感应电压触发快脉冲直线变压器驱动源(FLTD)中气体开关击穿延时过程,给出了击穿延时的估算公式。初步实验研究了FLTD用三电极气体开关在复合电压作用下的击穿特性,结果表明:在±70kV直流充电电压叠加300kV/30ns快脉冲电压的复合电压作用下,气体开关的击穿延时小于相同工作系数下常规触发方式的击穿延时,采用SF6气体绝缘时,击穿延时较常规触发方式减小了17%~30%;采用N2绝缘时,减小了约50%,开关工作系数为55%时,击穿延时抖动小于5ns;理论估算的复合电压下击穿延时与实测结果基本吻合。     

Investigation of GEM-Micromegas detector on X-ray beam of synchrotron radiation

To reduce the discharge of the standard bulk Micromegas and GEM detectors, a GEM-Micromegas detector was developed at the Institute of High Energy Physics. Taking into account the advantages of the two detectors, one GEM foil was set as a preamplifier on the mesh of Micromegas in the structure and the CEM pream- plification decreased the working voltage of Micromegas to significantly reduce the effect of the discharge. At the same gain, the spark probability of the GEM-Micromegas detector can be reduced to a factor 0.01 compared to the standard Micromegas detector, and an even higher gain could be obtained. This paper describes the performance of the X-ray beam detector that was studied at 1W2B Laboratory of Beijing Synchrotron Radiation Facility. Finally, the result of the energy resolution under various X-ray energies was given in different working gases. This indicates that the GEM-Micromegas detector has an energy response capability in an energy range from 6 keV to 20 keV and it could work better than the standard bulk-Micromegas.     

用于数码显微镜的白平衡校正方法

提出了一种用于数码显微镜的非线性白平衡方法.以标准D65光源光照下孟赛尔色卡每个色块的XYZ三刺激值和所成图像中的RGB值为训练样本,用神经网络建立不同数码显微镜拍摄的RGB输出与XYZ三刺激值之间的关系;再通过Estevens矩阵把XYZ三刺激值转换成人眼感光器所接受到的刺激值,并进行非线性计算;最后把计算结果转换回RGB空间,从而得到白平衡后的图像.实验结果表明,该方法所得的白平衡校正结果更加接近标准白光照射下的图像颜色.在光源色纯度较高的情况下,采用调整通道增益的方法变化幅度较大,而采用本文提出方法结果更加稳定;特别是当光源的色纯度过大使得图像中某个颜色通道的值接近0的时候,用调整三通道增益的方法已经完全失去了校正作用,而采用本文中的非线型方法仍然可以得到好的校正结果.同时,此方法中建立的神经网络模型反映的是成像设备的RGB空间到XYZ空间的转换特性,对于不同的光照条件,此特性不变,因此对于不同光源不需要分别建立神经网络模型.