针对基于傅里叶变换光正交频分复用(FFT-OFDM)的非正交多址可见光通信(NOMA-VLC)系统存在可靠性低、用户公平性差等问题, 提出将提升小波变换(LWT)作为载波调制方式, 建立基于LWT-OFDM的NOMA-VLC系统, 介绍了系统中的信号处理过程, 构建了5 m×5 m×3 m的室内空间实验环境。实验结果表明: 与基于FFT-OFDM的NOMA-VLC系统相比, 随着正交幅度调制方式的阶次由4增大到64, 所提系统的平均误码率达到阀值3.8×10-3时, 所需的信噪比(SNR)值较低, 至少低4.4 dB; 用户性能差异变化不明显甚至不变。

Among the lead-free piezoceramics, (1−x)BiFeO3−xBaTiO₃ (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature (TC>400∘C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO₃ and BaTiO₃, and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24h) of BiFeO₃ on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO₃ and BiFeO₃ powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO₃ increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO₃–0.3BaTiO₃ ceramics also improved. At the condition of a hydrothermal reaction time of 24h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant (Tkε=1.53×10−2/∘C between RT and 300∘C) and the highest Curie temperature (TC=471∘C at 100kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

交直流混合电力系统优化配置过程会受到光伏、风机出力不确定性的影响, 电力系统规划效果较差, 由此, 设计一个交直流混合电力系统中长期双层优化配置规划方法。将二元变量模型引入不确定模型中, 计算风、光资源对交直流混合微电网优化配置的影响参数, 计算交直流电力系统潮流, 设置目标函数与系统功率条件, 进行容量优化, 实现交直流混合电力系统中长期双层优化配置规划。实验结果表明, 所提出的规划方法提高了电压相角区间估计精度、电压幅值, 还降低了换流损耗与规划成本, 满足实际设计需求。

基于Pockels效应原理, 分别对交直流混合强电场传感器中的电光传感单元和电场调制机构进行了设计与测试。对电光传感单元结构进行合理设计, 选取并制备相关器件。搭建试验平台, 试验结果表明电光传感单元输入输出具有良好的线性度, 对电场波形的变化具有快速的响应且频率特性良好, 其性能满足测量调制后电场波形的需求。利用电光传感单元和电场调制机构组建传感器, 并测量了交直流混合强电场响应。

为优化水泥基复合材料的电学性能, 以碳纤维(CF)和钢纤维(SF)为导电材料, 通过抗压强度试验、交流阻抗测试、扫描电镜测试和升温试验, 研究了碳纤维和钢纤维的体积掺量对水泥基复合材料抗压强度和电学性能的影响。结果表明, 碳纤维-钢纤维水泥基复合材料的抗压强度随碳纤维掺量增大呈先增大后减小的趋势。碳纤维、钢纤维的渗滤阈值分别为0.35%和0.6%(均为体积分数), 复掺碳纤维和钢纤维使水泥基复合材料的导电性能大幅增强, 产生了明显的正向混杂效应, 碳纤维和钢纤维体积掺量达到渗滤阈值后, 继续增大纤维掺量对导电性能的提升作用不大。用ZSimp Win软件拟合得到等效电路各电路元件数值, 并结合SEM照片分析了导电机制。碳纤维-钢纤维水泥基复合材料具有良好的电热性能, 当输入功率为7.9 W, 通电30 min、60 min、90 min后, 其平均温度可达到33 ℃、43 ℃、50 ℃, 通过曲线拟合得到了温度随时间变化的回归方程。

针对运营商本地网核心汇聚节点少, 在面对专线业务快速开通需求时存在单个汇聚节点覆盖面积过大、无法快速实现业务接入汇聚, 以及多业务接入平台(MSAP)设备难以满足带宽迅猛增长的专线业务需求等问题, 结合接入型光传送网(OTN)的设备特点和专线业务需求等因素, 总结了接入型OTN设备的能力和成本优势, 提出了可行的接入型OTN设备组网部署的应用建议。

Monophasic and polycrystalline double perovskite Eu₂CoMnO₆ has been synthesized, and its structural characterization, frequency and temperature-dependent dielectric relaxation have been studied. Observed thermally activated dielectric relaxation was explained using the empirical Havriliak–Negami (HN) dielectric relaxation function with an estimated activation energy E∼ 0.22 eV and attempt frequency f0∼ 2.46 × 10⁹ Hz. The frequency-dependent AC conductivity data, over a wide range of temperature (100–325 K), followed the empirical universal power law behavior (∼fn, n is the constant exponent) showing two different frequency exponents, respectively, in the high- and low-temperature regions. The high-temperature (> 275 K) conductivity data followed the continuous time random walk (CTRW) approximation model proposed by Dyre. However, this model failed to reproduce the observed conductivity spectra in the low-temperature side (< 200 K). Interestingly, both the high- and low-temperatures’ conductivity data can be scaled to the master curve with suitably chosen scaling parameters.Monophasic and polycrystalline double perovskite Eu₂CoMnO₆ has been synthesized, and its structural characterization, frequency and temperature-dependent dielectric relaxation have been studied. Observed thermally activated dielectric relaxation was explained using the empirical Havriliak–Negami (HN) dielectric relaxation function with an estimated activation energy E∼ 0.22 eV and attempt frequency f0∼ 2.46 × 10⁹ Hz. The frequency-dependent AC conductivity data, over a wide range of temperature (100–325 K), followed the empirical universal power law behavior (∼fn, n is the constant exponent) showing two different frequency exponents, respectively, in the high- and low-temperature regions. The high-temperature (> 275 K) conductivity data followed the continuous time random walk (CTRW) approximation model proposed by Dyre. However, this model failed to reproduce the observed conductivity spectra in the low-temperature side (< 200 K). Interestingly, both the high- and low-temperatures’ conductivity data can be scaled to the master curve with suitably chosen scaling parameters.