Pressure dependences of elastic and lattice dynamic properties of AlAs from ab initio calculations

Ab initio calculations, based on norm-conserving nonlocal pseudopotentials and density functional theory (DFT), are performed to investigate the structural, elastic, dielectric, and vibrational properties of aluminum arsenide AlAs with zinc-blende (B3) structure and nickel arsenide (B8₁) structure under hydrostatic pressure. Firstly, the path for the phase transition from B3 to B8₁ is confirmed by analyzing the energies of different structures, which is in good agreement with previous theoretical results. Secondly, we find that the elastic constants, bulk modulus, static dielectric constants, and the optical phonon frequencies are varying in a nearly linear manner under hydrostatic pressure. What is more, the softening mode of transversal acoustic mode at X point supports the phase transition in AlAs.     

The pressure dependences of elastic and lattice dynamic properties of AlAs from ab initio calculations

Ab initio calculations,based on norm-conserving nonlocal pseudopotentials and density functional theory(DFT),are performed to investigate the structural,elastic,dielectric,and vibrational properties of aluminum arsenide(AlAs) with a zinc-blende(B3) structure and a nickel arsenide(B81) structure under hydrostatic pressure.Firstly,the path for the phase transition from B3 to B81 is confirmed by analyzing the energies of different structures,which is in good agreement with previous theoretical results.Secondly,we find that the elastic constants,bulk modulus,static dielectric constants,and the optical phonon frequencies vary in a nearly linear manner under hydrostatic pressure.What is more,the softening mode of the transversal acoustic mode at the X point supports the phase transition in AlAs.     

电子束产生大尺度等离子体过程的数值模拟研究

建立了一个四组分一维混合模型，对电子束注入大气产生大尺度等离子体的过程进行了数值模拟.结果表明了能量为140keV、流强为50mA/cm²的注入电子束，可以产生线度为0.5m，密度为10¹²cm^-3量级的大气环境下等离子体.电子束所伴随的空间电荷效应由于等离子体的产生会很快消失，不影响后续的等离子体产生过程.电子束注入流强主要影响产生等离子体的密度，而电子束能量则同时影响其空间线度和密度. 关键词： 电子束 碰撞 电离     

High longitudinal selectivity of shifting multiplexing in volume holograms

High longitudinal selectivity of the shifting multiplexing with spherical reference wave is proposed and demonstrated. A simplified method based on wave optics is used for calculating the selectivity, and the result fits well the experimental measurement. Under the paraxial condition, a simple formula for the longitudinal selectivity is introduced. With use of an object lens with effective NA=0.817, we obtain that an FWHM of selectivity is as small as 1 μm.     

多层光子晶体滤波器研究

从双层结构出发研究了一种由多块不同的单周期光子晶体组合而成的多层结构的滤波器，论述了这种滤波器的工作原理，研究表明这种结构适于制作带通、窄带通过、带阻、宽带带阻、高通以及其它各种性能的滤波器。实验和理论研究的结果相一致。     

Mössbauer effect of iron-57 intercalated in layered compound 2H−Fe0.5TaSe2

⁵⁷Fe Mössbauer effect study has been performed on intercalated compound 2H?Fe_0.5TaSe₂ over a temperature range between 14K and 500K. The highly concentrated intercalation samples 2H?Fe_xTaSe₂ with Fe atoms (x up to 2) are prepared by the electrochemical method for the first time. The Mössbauer measurement shows that iron is in Fe³⁺ high spin state and with the same probability occupies both octahedral and tetrahedral interstices of the Van der Waals gap. The fact that effective masses of iron ions in both sites are close to 57 amu and characteristic temperatures (Θ_M =130K, 107K respectively) are found to be relatively small is attributed to the weak forces on Fe³⁺.     

用信号处理技术及传播理论还原雷声频谱

以往关于雷声的研究都限于观测点雷声频域范围的探讨, 由于噪音和衰减因素的影响, 观测点的雷声频谱有很大失真. 针对在兰州地区观测的一次雷暴过程中的雷声信号, 利用数字信号处理技术,由观测点处的雷声音频信号得到频率谱,并对雷声频谱进行噪音分析; 然后结合声音在大气中传播的衰减理论, 分析了不同大气环境对声吸收的影响, 并推算出了声源附近的雷声频率谱. 关键词： 雷声频谱 信号处理 传播理论 峰值频率     

激光脉冲的横向波形对弓形波电子俘获的影响

用粒子模拟研究了在激光尾波场电子弓形波注入过程中激光脉冲的横向波形对尾波场俘获电子数目的影响, 发现与高斯激光相比, 超高斯形激光更有利于拉动空泡闭合前侧边的电子团向空泡尾部汇聚形成高能量局域化的弓形波, 从而导致更多的电子注入到空泡的加速相, 使得被俘获的电子数目提高近5倍, 且电子束品质得到改善.该研究对于进一步理解尾波场加速中电子注入等有参考价值. 关键词： 尾波场 电子俘获 横向波形 粒子模拟     

风机封闭系统内噪声模拟分析

风机系统工作时的一个突出问题是其进风口和出风口产生的噪声。由于风机流场非常复杂,以及实验成本、实验条件限制,基于计算流体力学（Computational Fluid Dynamics, CFD）的理论逐渐成为风机噪声估计的重要方法。本文拟通过对由风机及其冷却系统构成的封闭系统进行数值建模和仿真,判断出风机主要气动噪声源的位置和种类,为处于封闭系统内的风机的噪声大小预测,提供一个可供参考的信息。结果表明：风机出口腔体内部非定常压力波动强度最大。     

铁电存储器中高能质子引发的单粒子功能中断效应实验研究

利用中国原子能科学研究院的中高能质子实验平台,针对两款商用铁电存储器开展了中高能质子单粒子效应实验研究,发现其中一款器件在质子辐照下发生了单粒子翻转和单粒子功能中断.本文主要针对单粒子功能中断效应展开了后续实验研究.首先通过改变质子能量对器件进行辐照,发现单粒子功能中断截面随质子能量的提高而增加.为进一步研究器件发生单粒子功能中断的机理,利用激光微束平台开展了辅助实验,对铁电存储器的单粒子功能中断效应的敏感区域进行了定位,最后发现铁电存储器单粒子功能中断是由器件外围电路发生的微锁定导致的.