针对细微特征进行K-means聚类的电台分选识别技术

现代战场中的无线通信设备日益增多，精准获取个体信息已成为研究热点，但也是难点。针对通信电台，提出了一种分选识别技术。该技术从电台物理层特性出发，对其辐射信号的细微特征进行K-means聚类以实现分选，分选的同时提取各个个体的特征属性值，未知信号通过与特征属性值相关运算实现个体识别。该技术无需先验知识，无需训练运算，通过实验验证，其可行、高效，易于工程实现。     

认知双向中继网络在κ-μ衰落信道下的中断性能分析

针对认知双向中继网络在进行数据传输时面临的复杂无线信道场景问题,采用广义κ-μ分布构建认知双向中继网络中的视距和非视距无线传输信道,推导次网络在κ-μ衰落信道下的统一中断概率,并分析次网络在多种单一和混合衰落信道情况下的中断性能。仿真结果表明,无线信道的衰落程度对次网络的中断概率影响显著,依据衰落信道类型合理设置网络参数将有助于提升次网络中断性能。     

Improving the shelf life stability of vacuum-packed fresh-cut peaches (Prunus persica L.) by radio frequency heating in water

The present study aimed to investigate the influence of radio frequency (RF) heating at 70 and 80 °C, in comparison with the traditional conventional heating. The RF heating technology was applied for maintaining the colour and textural quality as well as inactivating the enzymatic activity of polyphenol oxidase (PPO) and reducing the Escherichia coli growth in packaged fresh-cut peach samples. To evaluate this, 120 g of freshly cut peach fruit was placed in heat-resistant plastic bags, and 50 mL of sugar solution (12°Brix) was added to each bag and vacuum-packed for conventional heating and radio frequency (RF) heating. Our results demonstrated that the RF heating process could reduce the heating time by up to 83% at 70 and 80 °C as compared to conventional heating. Moreover, RF heating at 70 and 80 °C reduced the PPO enzymatic activity, which caused enzymatic browning, up to 85.46% and 93.5%, respectively, as compared to 40.86% reduction only for conventional heating. Furthermore, RF heating completely inhibited E. coli growth. Collectively, we demonstrated that RF heating is an emerging and promising technology for improving the quality of fresh-cut fruits such as peach during various storage conditions. The present study provides relatively novel information on the effectiveness of RF heating in maintaining the quality of fresh-cut peaches. In the future, we would like to investigate the effectiveness of RF heating on other agricultural products.     

采用信道估计法的基站VSWR实时检测

为解决无线基站宽带工作频带内电压驻波比(Voltage Standing Wave Ratio,VSWR)的实时测量，提出了一种采用信道估计法的测量方案。该方案实现简单，在基带处理单元高速率位置发送数据，依次抓取射频通道反馈和反射数据，分别求取信道响应序列，结合工厂装备测试数据，计算驻波反射系数和反射点位置。发送信号采用宽带正交频分复用信号，能检测到工作频段内任何频点处的驻波异常。有用信号前加循环前缀，并引入峰值抵消核，能正确检测到多个反射点驻波。仿真结果表明，该方案驻波测量精度和单回波点位置精度达到预期，多回波点测量能抓准外部主要故障点，在基站VSWR实时测量中具有良好的应用前景。     

不同热处理方式对玉米醇溶蛋白特性的影响

研究了不同热处理方式(水浴、微波、射频)和处理终点温度(70、80、90℃)对玉米醇溶蛋白功能性质与结构的影响。结果表明:多种热处理均会提高玉米醇溶蛋白溶解度、乳化能力和巯基含量,且这3项指标随着处理终点温度的升高而升高,射频处理至90℃使玉米醇溶蛋白溶解度、乳化能力和巯基含量分别提高了74.65%、171.7%和53.94%。应用差示扫描量热法测定玉米醇溶蛋白变性温度,发现微波处理后蛋白质变性温度略有升高。此外,紫外光谱分析提示,玉米醇溶蛋白经微波和射频加热处理后,蛋白质分子结构舒展、基团暴露,这使得蛋白质的溶解性和乳化能力有所改善。傅里叶变换红外光谱分析发现热处理改变了玉米醇溶蛋白的二级结构,其中微波和射频处理效果更明显。     

黑胡椒颗粒的介电特性混合方程研究

通过介电混合方程对黑胡椒颗粒的介电特性进行推算,对比模拟值与实验值以验证介电特性混合方程的适用性。以黑胡椒颗粒为研究对象,测定压缩黑胡椒粉的介电特性,并运用介电特性混合方程-CRIME方程、LLLE方程、BE方程计算获得胡椒颗粒的介电特性,随后运用COMSOL Multiphysics软件建立静电场-热传导双向耦合模型对射频加热仿真,并通过27.12MHz,12 k W的平行极板式射频系统进行加热实验验证。采用CRIME方程获得的胡椒颗粒介电特性运用在仿真中与试验结果温度分布为最接近。作者证明了通过压缩胡椒粉末介电特性代入CRIME方程能够有效获得黑胡椒颗粒的介电特性,这有助于工业生产中颗粒物料射频加热工艺的研发。     

Effect of lactose content on dielectric properties of whole milk and skim milk

Dielectric properties (dielectric constant ε′ and dielectric loss factor ε′′) of whole milk and skim milk with the lactose content of 4.56–6.44% and 4.57–6.47%, respectively, were measured over the frequency range of 20–4500 MHz at 25 °C using a vector network analyzer. The results showed that ε′ decreased with increasing frequency, and ε′′ changed with V shape and its minimum was noted at about 2000 MHz. Whole milk had lower dielectric properties than skim milk at almost same lactose content and a given frequency. ε′ had weak positive linear relationship with lactose content for whole milk, but had negative linear relationship for skim milk. No matter for which milk, ε′′ had very good negative linear relationship with lactose content below 1000 MHz and had good positive linear relationship above 2300 MHz. The study provides information on developing rapid lactose detector for milk in future.     

基于星座图对射频指纹识别方法的研究

针对星座图的射频(RF)指纹识别方案中,低信噪比环境下识别准确率低的问题,提出一种基于欧式距离与幅度距离的二维识别算法来进行RF指纹识别。该方案通过对星座图进行优化处理,可从优化后的星座图中提取识别性能更好的RF指纹,再通过二维识别算法来提高识别准确率。仿真结果表明:与仅用欧式距离作为判断依据的方法相比,所提出的二维识别算法的识别准确率最高可提升8%,在设备容量为50组的情况下识别准确率为77.8%,并且从优化后的星座图中所提取的RF指纹具有更好的唯一性和稳定性。     

射电望远镜主动面促动器的电磁辐射分析

主动面控制技术是当前大口径、高精度射电望远镜广泛使用的主动补偿技术,其包含的促动器在补偿面形精度的同时也辐射电磁波并影响射电天文观测。文中结合目前研究现状,对极低电磁辐射要求下的促动器进行辐射源分析,重点针对促动器控制板上信号建立数学模型,并选取晶振回路计算,合理设定印制板及器件的参数,通过Ansys 软件进行频域有限元分析,得到控制板晶振回路的辐射结果和规律。用近场测试验证了文中方法的有效性。该研究为促动器控制板的电磁兼容优化设计提供了验证方法,为降低主动面控制系统的电磁辐射奠定了基础。