MOSFET调制器的实验研究

 介绍了MOSFET调制器的基本原理,并对其并联分流和感应叠加两种开关结构进行了实验研究。基于可编辑逻辑器件设计了其触发电路,驱动电路采用高速MOSFET对管组成的推挽输出形式,加快了MOSFET的开关速度。利用Pspice软件对开关上有无剩余电流电路(RCD)两种情况进行仿真,结果表明,加装RCD电路可以有效吸收MOSFET在关断瞬间产生的反峰电压。实验中,电流波形用Pearson线圈测量,用3个MOSFET并联作开关,当电容充电电压为450 V,负载为30 Ω时,脉冲电流13 A,前沿20 ns,平顶约80 ns;用3个单元调制器感应叠加,当电容充电电压为450 A,负载为30 Ω时,脉冲电流强度为40 A,前沿25 ns,平顶约70 ns。     

用于实时溅射深度测量的新型Grimm辉光放电光源的设计

采用辉光放电光谱仪进行物质表面深度分析时,样品溅射深度是重要的分析信息.本文设计了一种新型Grimm辉光放电光源,此光源与激光位移测距传感器构成的测昔系统可对样品溅射深度进行实时测量,并保证了良好的辉光溅射效果和分辨多层结构及界面的能力.采用激光三角测量技术,在辉光光谱分析的同时对溅射深度进行实时测量,能够有效地解决传统深度分析方法中步骤繁琐以及对深度估算不准确等问题.本光源采用光纤将辉光光谱信号从光源传至多道分光光电检测系统,在结构上首次实现了元素光谱信号和溅射深度信号的实时采集及基于时间的同步分析,对标准样品得到了理想的实时溅射深度测量曲线.本文详细介绍了此新型辉光放电光源的设计思路和工作原理.本辉光放电光源具有良好的深度分辨率,在30 mA,900 V,20 min的溅射条件下,对铁基和铜基样品的溅射速率分别约为10和55 nm·s-1,文中给出了样品的溅射坑表面形貌图和溅射坑显微照片.对中低合金钢标准样品进行了分析精密度实验,分析精度良好,其中C,Cu,Al,Ni,Mo,Mn,V元素相对标准偏差(RSD)均小于1.7%.Cr和Si元素RSD小于2.6%,给出了实测数据.     

A high-efficiency spin polarizer based on edge and surface disordered silicene nanoribbons

Using the tight-binding formalism, we explore the effect of weak disorder upon the conductance of zigzag edge silicene nanoribbons (SiNRs), in the limit of phase-coherent transport. We find that the fashion of the conductance varies with disorder, and depends strongly on the type of disorder. Conductance dips are observed at the Van Hove singularities, owing to quasilocalized states existing in surface disordered SiNRs. A conductance gap is observed around the Fermi energy for both edge and surface disordered SiNRs, because edge states are localized. The average conductance of the disordered SiNRs decreases exponentially with the increase of disorder, and finally tends to disappear. The near-perfect spin polarization can be realized in SiNRs with a weak edge or surface disorder, and also can be attained by both the local electric field and the exchange field.     

A study of sound intensity control for active noise barriers

Active noise control systems have been applied to increase the insertion loss of noise barriers where the squared sound pressure or the total acoustic energy density is used as the cost function in previous works. The absolute value of the mean active sound intensity is chosen as the cost function to obtain extra sound insertion loss in the dark area of a hybrid active noise barrier system in this note. The strategy of minimizing the near-field sound intensity at discrete locations along the edge of the passive barrier is shown to be able to provide better far-field noise reduction than that of minimizing the squared sound pressure control. Both numerical simulations and off-line experiments are carried out with a three-channel demonstration system, where the locations of the secondary sources and the error sensors are optimized and comparisons are made between the extra sound pressure attenuation of the sound intensity control and that of the squared sound pressure control.     

多速率STFT超宽带信号瞬时频率估计研究

提出多速率短时傅里叶变换(Multi Rate Short Time Fourier Transform,MR-STFT)瞬时频率估计算法,提高了超宽带信号瞬时频率估计精度。该方法将多速率信号处理算法与短时傅里叶变换(STFT)技术相结合,兼顾采样频率和被测频率,将宽频范围进行分段采样,对分段处理结果进行拟合,构成多速率STFT算法,实现超宽带信号瞬时频率的高精度测量。论文通过对仿真信号和实测信号进行处理,研究了方法的可行性和频率估计精度,结果表明MR-STFT算法较大提高了超宽带信号瞬时频率估计精度,尤其对低信噪比的超宽带信号效果显著。     

Theoretical studies on structure and performance of [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine‐based derivatives

Based on energetic compound [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine, a series of functionalized derivatives were designed and first reported. Afterwards, the relationship between their structure and performance was systematically explored by density functional theory at B3LYP/6‐311 g (d, p) level. Results show that the bond dissociation energies of the weakest bond (N–O bond) vary from 157.530 to 189.411 kJ · mol^?1. The bond dissociation energies of these compounds are superior to that of HMX (N–NO_2, 154.905 kJ · mol^?1). In addition, H1, H2, H4, I2, I3, C1, C2, and D1 possess high density (1.818–1.997 g · cm^?3) and good detonation performance (detonation velocities, 8.29–9.46 km · s^?1; detonation pressures, 30.87–42.12 GPa), which may be potential explosives compared with RDX (8.81 km · s^?1, 34.47 GPa ) and HMX (9.19 km · s^?1, 38.45 GPa). Finally, allowing for the explosive performance and molecular stability, three compounds may be suggested as good potential candidates for high‐energy density materials. Copyright © 2016 John Wiley & Sons, Ltd.     

考虑时滞效应与均值-方差效用的非零和投资与再保险博弈

在考虑时滞效应的影响下研究了非零和随机微分投资与再保险博弈问题.以最大化终端绝对财富和相对财富的均值-方差效用为目标,构建了两个相互竞争的保险公司之间的非零和投资与再保险博弈模型,分别在经典风险模型和近似扩散风险模型下探讨了博弈的Nash均衡策略.借助随机控制理论以及相应的广义Hamilton-Jacobi-Bellm...     

Mechanical, vibrational, and dynamical properties of amorphous systems near jamming

Amorphous systems undergo the jamming transition when the density increases, temperature drops, or external shear stress decreases, as described by the jamming phase diagram which was proposed to unify different processes such as the glass transition, random close packing, and yielding under shear stress. At zero temperature and shear stress, the jamming transition occurs at a critical density at Point J. In this paper, we review recent studies of the material properties of marginally jammed solids and the glassy dynamics in the vicinity of Point J. As the only singular point in the jamming phase diagram, Point J exhibits special criticality in both mechanical and vibrational quantities. Dynamics approaching the glass transition in the vicinity of Point J show critical scalings, suggesting that the molecular glass transition and the colloidal glass transition are equivalent in the hard sphere limit. All these studies shed light on the long-standing puzzles of the glass transition and unusual properties of amorphous solids.     

羊八井太阳中子望远镜和中子监测器对2005年1月20日GLE事件的探测

西藏羊八井位于东经90.53°, 北纬30.11°, 海拔4310m, 垂直地磁截止刚度14.1GV. 2005年1月20日羊八井太阳中子望远镜和中子监测器探测到与X7.1/2b太阳耀斑相关的GLE事件, 其中太阳中子望远镜能量>40MeV的能道在5min(07:00—07:05UT)和20min(07:00—07:20UT)的时间间隔内计数率增长的统计显著性分别是3.7σ和6.0σ, 同时羊八井中子监测器也探测到计数率的增长,初始时间为06:51—06:52UT. 观测表明在这次GLE事件中太阳质子可被加速到能量大于10GeV.     

利用可调谐半导体激光光谱技术对含尘气体中NH3的测量

利用可调谐半导体激光吸收光谱技术(TDLAS)并结合波长调制,在近红外波段1531.7nm处对常温常压下的NH3进行浓度测量.在10 m的长程吸收池内得到了25×10-6的浓度信号,并且在25×10-5-400×10-6浓度范围内二次谐波信号与浓度具有良好的线性关系.讨论了粉尘颗粒对于二次谐波信号的干扰,并提出了利用激光强度线性拟合解决颗粒对气体测量干扰的方法.