沙尘对沙漠边缘地区WCDMA信号的影响

首先结合阿拉尔市地形和建筑特点提出了一个改进的路径损耗传播模型;改进的模型中提出了沙尘因子的概念,考虑了沙尘暴对无线信号的影响;通过在沙尘天气对WCDMA基站天线发送信号的强度进行测量,并与无沙尘时测量的信号强度进行比较,使用MATLAB软件进行数据拟合得到沙尘因子,数据显示沙尘因子不仅与能见度有关,与距离基站的距离也存在一定的关系.最后针对模型进行优化前后的仿真比较,结果表明,优化后的模型更接近实际传播环境,沙尘因子的引入对移动通信传输系统的设计和布网有很大的指导意义.     

一种基于改进Logitic映射的跳频序列生成算法

在扩频序列生成算法中,针对周期抽取算法平衡性和比特重排算法稳定性的欠缺,基于改进的Logitic映射,结合采用比特抽取和扰动的方法,提出了一种改进的算法来构造跳频序列, 提出的算法不需要考虑与其他映射或者序列进行同步的问题,很大程度上缩减了迭代次数。仿真结果表明,提出的算法可以提供相关性更加优良的序列,且均匀性、平衡性上优于周期抽取比特重排算法,汉明相关性与理论参考值近似重合。     

突防任务中组网雷达干扰资源分配研究

基于突防飞机的位置构建了干扰效果评估指标,综合考虑突防飞机在整个突防过程中的位置变化时的干扰效益,利用概率加权法确定最终的目标函数,采用蚁群算法求解出干扰分配决策。仿真结果表明,该文提出的干扰效果评估指标可以很好地解决干扰资源分配问题,对实际作战指挥有一定的指导意义。     

基于”8”字形光纤谐振环全光纤MZI型梳状滤波器的设计与实验研究

为改善常规全光纤马赫-曾德尔干涉仪(MZI)型 滤波器的输出特性,提出了由2个2×2光纤耦合 器和1个”8”字形光纤谐振环级联组成全光纤MZI型梳状滤波器的设计方案。根据基本结构 ,应用光纤 传输理论和矩阵理论,得到滤波器输出谱的表达式,对其特性进行数值模拟分析,结果表明 :当耦合器分光 比取一些定值时,可得到输出波形通带平坦、形态近似于方波的梳状谱图,其25dB截止带带宽和0.5dB通 透带带宽明显改善,其值分别为26.2GHz和38.4GHz;器件具有一定的抗偏差能力 降低了制作难度,传输损耗对滤波器消光特性的影响较小。实验结果与理论分析相吻合。     

基于双耦合器的全光纤不等带宽波长交错滤波器的设计

为提高波长交错滤波器(interleaver)带宽的利用 率,提出了基于一字型3×3和2×2光纤耦合器组成 全光纤马赫-曾德尔干涉仪(MZI)型不等带宽波长交错滤波器(interleaver)的设计方案。运 用光纤传输理论 和矩阵理论,得到滤波器输出谱的表达式;依据傅里叶级数的理论,优化选择器件的结构参 数;数值 模拟分析了器件的输出特性。结果表明:两个耦合器的耦合系数和光纤干涉臂长差取一些定 值时,器 件主要的两路输出带宽不等,它们的3dB带宽分别为31.5和 65.6GHz,满足不同传输速率10和40Gbit/s对带宽的要求,较等带宽interle aver有更高的利用率;通过分析器件结构参数对输出谱的影 响,发现器件具有一定的抗偏差能力;与普通的级联MZI型interleaver相比,新型器件的优 点是耦合 器少,在实际制作时可准确控制和检测耦合器的分光比,从而降低了制作难度。实验结果与 理论分析相吻合。     

大功率LED散热回路热管的实验研究

大功率LED热问题是制约大功率 LED的稳定性、可靠性和寿命的技术瓶颈之一,有效的低热阻封装LED热设计是提高LE D性能的关键。本文提 出一种应用于大功率LED散热的铜-水回路热管(LHP),研究了加热方 式、充液率、风压和倾角 等对LHP均温性、起动性和热阻等的影响。研究结果表明:在输入功率为30W时,LHP的启动时间约为 6.5min;热阻范围为0.48～1.62K/W;在热 负荷为30W时,蒸发器的温度可以稳定控制在75℃以下;蒸发器表 面均温差被控制在1.6℃以下;LHP的最佳的充液率为60%;冷凝器侧 风压在一定范围内(小于130Pa)时,冷凝器侧风压力越大,LED产 品的散热性能越好。     

Phenol-formaldehyde resin route to the synthesis of several iron group transition metal phosphides

Abstract

A series of iron, cobalt and nickel metal phosphides of chemical formula Fe_xP, Co₂P and Ni₂P with high specific surface areas of 331.1, 294.2 and 228.0 m² g^?1, respectively, was firstly synthesized by phenol-formaldehyde resin route. It was found that the as-prepared Co₂P and Ni₂P samples synthesized using phenol-formaldehyde resin as a carbon source showed much higher BET surface areas than those prepared using other carbon sources reported before, including cinnamic strong alkali anion exchange resin, p-phenylenediamine and hexamethylenetetramine. This phenol-formaldehyde resin route was proved to be as universal as traditional H₂ reduction method.     

STUDIES ON ORGANOPHOSPHORUS COMPOUNDS XLIV. STRUCTURAL EFFECT OF ELECTROPHILES ON THE REGIOSELECTIVITY OF CARBANION DERIVED FROM DIALKYL ALLYLPHOSPHONATES

Abstract

For the evaluation of the structural effect of electrophiles on the regioselectivity of ambident anions, the reaction of phosphoryl allylic carbanion with p-substituted benzaldehydes was investigated.     

Direct electrochemistry of hemoglobin on graphene/Fe3O4 nanocomposite-modified glass carbon electrode and its sensitive detection for hydrogen peroxide

Graphene/Fe₃O₄ nanocomposite was prepared for the immobilization of hemoglobin (Hb) to improve the electron transfer between Hb and glass carbon electrode (GCE). The characterization of nanocomposites was described by transmission electron microscopy, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The electrochemistry of Hb on the graphene/Fe₃O₄-based GCE was investigated by cyclic voltammetry and amperometric measurement. The modified electrode showed a wide linear range from 0.25 μmol/L to 1.7 mmol/L with a correlation coefficient of 0.9967. The detection limit of the H₂O₂ biosensor was estimated at 6.0?×?10^?6?mol/L at a signal-to-noise ratio of 3.     

Facile electrochemical synthesis of a conducting copolymer from 5-aminoindole and EDOT and its use as Pt catalyst support for formic acid electrooxidation

5-Aminoindole and 3,4-ethylenedioxythiophene (EDOT) were copolymerized electrochemically on a carbon cloth (CC) electrode in an aqueous sulfuric acid solution. The as-prepared copolymer was characterized by cyclic voltammogram, SEM, and UV-vis and FT-IR spectra through which the electrochemical properties, structure, and composition of the as-obtained copolymer were determined. The electrochemical activity and stability of the as-formed copolymer are significantly improved in comparison with poly(5-aminoindole) due to the incorporation of EDOT units into the conjugated chain. The copolymer film-modified CC electrode was used as substrate for Pt particle deposition (denoted as Pt/copolymer/CC), and then, its catalytic activity towards formic acid electrooxidation was studied. Experimental results indicate that the catalytic activity of Pt/copolymer/CC towards formic acid electrooxidation is enhanced in comparison with that of Pt/homopolymer/CC, which can be attributed to the homogeneous distribution of Pt nanoparticles on the copolymer/CC substrate and the improved electrochemical activity of the copolymer film.