基于GPS的射电望远镜跟踪平台的研究

现今,大型的射电望远镜项目在各个国家都得到了普遍的重视。但是,市场上需求越来越多的是小型的射电望远镜或者科普类的射电望远镜。大型的射电望远镜天线,指向精度要求高,观测的过程中需要做各种实时修正,允许投资较多于控制模块,大多采用计算机闭环程序控制。虽然在大型的射电望远镜上这样的控制方法取得了很好的效果,但是对于小型的射电望远镜来说昂贵和复杂的闭环控制方式并不是适用。所以,本文通过实践调研,通过按键控制电路来控制单片机的工作模式来代替原来庞大的控制台,并经过大量的调试,实现了可适用于小型天线的控制系统。     

宽带电力线载波通信技术在用电信息采集系统中的应用

低压电力线载波通信技术由于具有零施工、无辐射、电力公司专有的特点,在用电信息采集系统建设中得到了高度重视。随着载波通信技术的发展,宽带载波通信技术日臻成熟,由于具有速度快、路由性能强、抗噪声能力出色等优势,因此具有广泛的应用前景。文章针对目前用电信息采集系统的主流本地通信技术进行分析,论述各自优劣,对宽带电力线载波通信技术的应用前景进行了研究和分析。     

基于因子回归分析和分层雷达图法的电动汽车运行状态评估

为优化电动汽车的检修策略,有必要利用监测数据对其运行状态进行综合评估。选取蓄电池、电机传动和充放电过程的26个特征量作为电动汽车运行状态指标,利用因子分析法提取指标的公共因子,利用公共因子间的独立性对电动汽车状态指标进行分类;再结合逐步回归分析对各个分类的指标进行筛选,删除对评估结果影响小的指标,由此建立电动汽车运行状态综合评估指标体系。将针对电动汽车评估的层次递阶结构,采用分层雷达图法对电动汽车运行状态进行综合评估。根据某电动公交车充电站的监测数据进行计算,结果表明所提方法能够反映电动汽车各组成部分及整体运行状态,所提出的评估模型和方法是正确和有效的。     

考虑事故后频率约束的两阶段经济调度

为了保证事故后电力系统仍能正常运行,基于多阶段决策的思想提出了考虑事故后频率约束的两阶段随机经济调度模型。该模型中同时考虑事故前(第一阶段)和事故后(第二阶段)系统的运行成本,分别称为"当前成本"和"未来成本"。第一阶段的优化目标函数考虑在满足供电可靠性的条件下使常规机组和风电机组的发电成本最小;为了保证系统频率在事故后较短时间内恢复正常,第二阶段考虑了对低频减载的约束,目标函数为常规机组和风电机组的发电成本,风能高估低估的惩罚成本以及减负荷的惩罚成本最小。针对模型的非光滑性,采用光滑化方法对其进行处理,并以IEEE30节点系统进行仿真,仿真结果验证了新模型和算法的有效性。     

Mild functionalization of carbon nanotubes filled epoxy composites: Effect on electromagnetic interferences shielding effectiveness

The effect of nitric acid mild functionalized multiwalled carbon nanotubes (MWCNTs) on electromagnetic interference (EMI) shielding effectiveness (SE) of epoxy composites was examined. MWCNTs were oxidized by concentrated nitric acid under reflux conditions, with different reaction times. The dispersion of MWCNTs after functionalization was improved due to the presence of oxygen functional groups on the nanotubes surface. Functionalization at 2 h exhibits the highest EMI SE and electrical conductivity of MWCNTs filled epoxy composites. However, EMI shielding performance of MWCNTs filled epoxy composite declined when the functionalization reaction time was prolonged. This was due to extensive damage on the MWCNT structure, as verified by a Raman spectroscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42557.     

Microstructure,Thermal Conductivity,and Electrical Properties of In Situ Pressureless Densified SiC–BN Composites

The microstructure, thermal conductivity, and electrical properties of pressureless densified SiC–BN composites prepared from in situ reaction of Si₃N₄, B₄C, and C were systematically investigated, to achieve outstanding performance as substrate materials in electronic devices. The increasing BN content (0.25–8 wt%) in the composites resulted in finer microstructure, higher electrical resistivity, and lower dielectric constant and loss, at the expense of only slight degradation of thermal conductivity. The subsequently annealed composites showed more homogeneous microstructures with less crystal defects, further enhanced thermal conductivities and electrical resistivities, and reduced dielectric constants and losses, compared with the unannealed ones. The enhanced insulating performance, the weakened interface polarization, and the reduced current conduction loss were explained by the gradual equalization of dissolved B and N contents in SiC crystals and the consequent impurity compensation effect. The schottky contact between graphite and p‐type SiC grains presumably played a critical role in the formation of grain‐boundary barriers. The annealed composites doped with 8 wt% BN exhibited considerably high electrical resistivity (4.11 × 10¹¹ Ω·cm) at 100 V/cm, low dielectric constant (16.50), and dielectric loss (0.127) at 1 MHz, good thermal conductivity [66.06 W·(m·K)^?1] and relatively high strength (343 MPa) at room temperature.     

Evaluation of high temperature polymers in nanolayered films and gradient refractive index (GRIN) lenses

A new polymer nanolayer gradient refractive index (GRIN) system with more robust thermal stability because of incorporation of a high glass transition temperature polyester, OKP4HT, was demonstrated. A combination of extruded nanolayered GRIN film systems, comprised of five unique polymer materials, were combined to produce laminate optics comprised of a large internal refractive index gradient distribution, n = 1.445 – 1.630, without degradation of optical transmissive properties. The optical performance of a series of varied magnitude GRIN lenses, ranging from Δn = 0 to 0.185, was evaluated. Increasing the lens refractive index range resulted in decreased optic sphericalaberrations that followed analytical predictions. An analytical approach was reported to correlate the polymer material upper service temperature (UST) to the onset of polymer material loss modulus as measured by DMTA. Thermo‐optical interferometry measurements of irreversible lens deformation confirmed the lenses UST at 125°C for the OKP4HT/PC system as compared to 75°C for a PMM/SAN17 system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42741.     

Far‐Red‐Emitting BiOCl:Eu3+ Phosphor with Excellent Broadband NUV‐Excitation for White‐Light‐Emitting Diodes

Rare‐earth ion‐doped semiconducting phosphor has attracted extensive attention due to the ability to achieve efficient luminescence through the host sensitization. Here, we present a new type red‐emitting Eu³⁺ ‐doped BiOCl phosphors possessing a broad excitation band in the near‐ultraviolet (NUV) region. Experimental measurements and theoretical calculations confirm that Eu³⁺ ion dopants result in forming impurity energy level near valence band, and the excellent broadband NUV‐exciting ability of Eu³⁺ ion is due to the electronic transitions of BiOCl band gap. Moreover, the highest emission intensity of the phosphors is from the ⁵D₀ → ⁷F₄ transition of Eu³⁺ around 699 nm (far‐red) through whether host excitation or direct Eu³⁺ ions excitation, which lie in the particular structure of BiOCl crystals. Our results indicate that the Eu³⁺ ‐doped BiOCl crystals show great potential as red phosphors for white‐light‐emitting diodes.     

单因子老化中定子线棒等温松弛电流的研究

为研究电机定子线棒老化后的绝缘特性,制备了按实际线棒尺寸比例缩小的线棒试样,并对其进行了单独的热、电老化实验,后测量了不同老化程度线棒试样的等温松弛电流,并基于等温松弛理论研究分析了线棒绝缘内的陷阱分布变化。结果表明:线棒绝缘在冷热循环老化过程中存在"后固化"的现象,绝缘内陷阱密度先增加后减小;而在电老化过程中,试样绝缘内浅能级陷阱密度增加。根据不同极化过程对等温松弛电流的贡献,建立了定子线棒等温松弛电流的三阶指数衰减模型。研究表明,电机线棒老化的主要表现是环氧树脂和云母之间界面中缺陷的增加,而三指数衰减模型对等温松弛电流数据的拟合结果也足够准确。     

一种新型的同塔双回输电线路工频阻抗参数测量方法

基于输电线路三相不平衡及感应电压干扰在短时间不变的前提,提出了一种新型的同塔双回输电线路工频阻抗参数测量方法。该方法采用单相电源多变换接入的方式对不对称线路进行分相解耦测量,通过建立数学模型、数据拟合和矩阵变换,从而获得单回或两回线路的序阻抗及各序之间的耦合阻抗。该方法克服了高感应电压及三相不平衡对线路参数测试的影响,具有简单、精确、稳定等特点,测试结果表明了本文方法的有效性。