新型树状单分子磷-氮膨胀阻燃剂的合成及阻燃性能研究

以六氯环三磷腈、对羟基苯甲醚、新戊二醇以及三氯氧磷等为原料, 合成一种新型树状单分子磷-氮膨胀阻燃剂六(4-(5,5-二甲基-1,3-二氧杂环己内磷酸酯基苯氧基))环三磷腈(Ⅵ). 标题化合物结构经IR、MS 及¹H NMR 证实. 热失重分析表明标题化合物具有较高的热稳定性和良好的成炭性, 氮气氛下的起始分解温度为270 ℃, 600 ℃时炭残余量达45.2%. 实验表明, 标题化合物对环氧树脂呈现出良好的阻燃效果.     

Electronic and structural properties of N-vacancy in AlN nanowires: A first-principles study

The stability and electronic structures of AlN nanowires with and without N-vacancy are investigated using firstprinciples calculations.We find that there is an inverse correlation between formation energy and diameter in ideal AlN nanowires.After calculating the formation energies of N-vacancy at different sites in AlN nanowires with different diameters,we find that the N-vacancy prefers to stay at the surface of the nanowires and it is easier to fabricate them under Al-rich conditions.Through studying the electronic properties of AlN nanowires with N-vacancies,we further find that there are two isolated bands in the deep part of the band gap,one of them is fully occupied and the other is half occupied.The charge density indicates that the half-fully occupied band arises from the Al at the surface,and this atom becomes an active centre.     

Magnetotransport properties of two-dimensional electron gas in AlGaN/AlN/GaN heterostructures

Magnetotransport measurements are carried out on the AlGaN/AlN/GaN in an SiC heterostructure, which demonstrates the existence of the high-quality two-dimensional electron gas (2DGE) at the AlN/GaN interface. While the carrier concentration reaches 1.32 × 10¹³ cm ^{- 2} and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21 × 10⁴ cm²/(V·s) at 2 K. The Shubnikov—de Haas (SdH) oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEG is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.     

High temperature characteristics of AlGaN/GaN high electron mobility transistors

Direct current (DC) and pulsed measurements are performed to determine the degradation mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas (2DEG). The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.     

高频表面波雷达发射天线及其对输入信号要求的研究

高频表面波雷达因具有反隐身、抗反辐射导弹和超视距探测等特性而受到广泛重视。本文从提高雷达发射天线的增益出发,采用矩量法对对数周期偶极天线及扇形阵进行了理论分析,给出了它们的仿真图形,并在此基础上讨论了阵元输入激励的偏差对阵列方向图的影响,这对高频表面波雷达发射天线的设计具有一定的指导意义。     

VACON变频器在直驱型风力发电系统独立变桨中的应用可行性分析

直驱型风力发电系统是一种应用前景看好的变速恒频风力发电方案,为提高风能的利用率和风力发电经济效益,提高系统稳定性降低维修成本,迫切要求对风力机进行独立变桨控制。本文介绍了直驱型风力发电系统的拓扑原理和风力机的特性曲线,并以基于同步电动机的变桨执行机构为平台,介绍了Vacon NX型变频器的控制功能,并对其在独立变桨场合的应用可行性进行了分析,由Vacon NX系列变频器的各项参数和性能指标可知,其应用于变桨控制中是可行的,是实现高效、可靠独立变桨控制的良好途径之一。     

规范正交梯形结构对数域滤波器

提出了一种基于规范正交梯形网络信号流图模拟的对数域滤波器设计方法.能直接对给定的任意高阶传输函数进行综合.用该方法设计了1dB波纹三阶椭圆埘数域低通滤波器.Pspice仿真表明,所设计的滤波器实际频响特性几乎是理想的,而且具有电路结构简单、需要的元件数少、灵敏度低和最优的动态范围等特性.     

激光二极管准直中非球面透镜的应用

激光二极管(LD)准直打线的过程中,影响线宽的主要因素主要有:准直透镜的像差、焦距以及准直透镜后面柱面镜的曲率半径。主要分析了准直透镜对LD准直打线性能的影响。首先用Zemax软件模拟了非球面透镜和球面透镜组在LD准直打线的性能;并用高斯光传播公式在不考虑像差的情况下推导出线宽和透镜焦距的关系;最后对9款不同焦距的LightPath非球面透镜进行了LD准直打线的实验。实验结果表明与计算结果基本相符,并且在小像差系统中线宽与准直透镜的焦距成反比关系。     

一种新型亚胺基吡啶铁配合物和茂金属复配催化乙烯原位共聚制备LLDPE

20世纪80年代中期,Kissin等人^[1]首先采用了乙烯二聚催化剂和传统Ziegler-Natta催化剂组成双功能催化体系,催化乙烯原位聚合制备短支链线性低密度聚乙烯(LLDPE)．由于该方法具有不需要另外加入α-烯烃的特点,近年来受到人们的重视．胡友良^[2-4]等人用乙烯二聚催化剂Ti-     

流动注射-化学发光测定环境样品中的痕量铜

本文基于Cu2+与贮备铁氰化钾及鲁米诺在碱性条件下产生化学发光的原理,建立了一种新的测定痕量铜的化学发光方法。方法的相对标准偏差小于5.0%,线性范围为5.0×10-9～1.0×10-7mol/L,检出限(S/N=3)为8.0×10-10mol/L。用本法成功地实现了对环境样品中痕量铜的定量分析。