基于峰值点的目标对准在MSTAR SAR图像分类中的应用

模板匹配的分类方法是合成孔径雷达目标识别的重要方法。研究了MSTAR SAR图像,指出图像中的目标峰值点本质上对应于实际物体的散射中心,并且在一定方位区间中具有稳定性。假设目标存在位置偏移的基础上,提出先利用目标峰值点对准目标,再生成模板和分类的思想。分析了方位区间中基准图像的选取及对准过程对模板生成和目标分类的影响程度。最后研究了同类变形目标间的分类,提出了峰值点特征增强成像、预分类、目标对准和正式分类的四步算法。结果证明,所提算法具有较高的分类精度和效率。     

脉冲爆震火箭发动机引射模态的起爆实验研究

为实现脉冲爆震火箭发动机(PDRE)引射模态下主爆震室的起爆,采用航空煤油和氧气作为推进剂,设计了PDRE引射模态的模型机,采用压电传感器测量主爆震室中爆震波的压力和速度.在主爆震室中成功实现了5 ～8Hz稳定连续的爆震,爆震波的峰值压力能够达到3MPa,爆震波以1600～ 2000m/s左右的速度在主爆震室中传播.实验结果表明:PDRE引射模态下主爆震室的DDT距离,远低于常规高能电喷起爆下的两相PDRE的DDT距离;高频PDRE引射模态下主爆震室的起爆难度加大;加长主爆震室、末端增加收敛段可以提高引射模态的爆震性能.     

基于频谱仪的脉冲调制信号功率校准技术研究

脉冲调制信号是雷达和数字通信系统中的一类重要信号。本文主要研究脉冲调制信号的功率测量方法,讨论并分析了脉冲调制信号的频谱特点,提出使用频谱分析仪实现脉冲调制信号的平均功率和峰值功率的测量,并采用正弦调幅法对频谱分析仪的测量结果进行验证。实验表明使用频谱仪测量脉冲调制信号功率简单易行且具有较高的测量精度。     

Options for mapping foF2

Available long-term and near-real time global and regional maps of foF2 are examined in relation to telecommunication and aeronomy requirements and recommendations are made for the best present-day maps to adopt. In particular, it is shown that current CCIR maps do not meet all requirements and should not necessarily be regarded as standards against which other mappings should be compared.     

几种常用步态检测典型算法的设计比较

基于步态检测技术是影响行人导航定位系统精度的一项关键因素,在研究了相关行人导航文献后,对行人步行状态建立模型,并选取了三种常见的步态检测算法,峰值检测算法、自适应峰值检测算法和零点检测算法,介绍分析了这几种算法的基本原理和设计思路。随后,在相同的环境下,基于同样的设备和测试者,设置几组不同的步行状态,分别使用三种算法对行人的运动步数进行测试统计。最后,比较测试结果,分析说明了三种算法的精确度以及各自的优缺点。     

检波器谐振频率数学模型及其频响误差的修正

峰值检波器的频响误差在高频段主要是由分布参数产生的高频谐振误差。本文利用实测数据建立了检波器谐振频率数学模型，根据模型的预测值对检波器和了频响误差修正。计量检定表明修正后的频响误差大大减小。     

一种实现太阳阵峰值功率跟踪的智能控制方法

首先讨论了峰值功率跟踪的一般概念及原理,然后提出了一种采用模糊自寻优智能控制原理实现太阳阵峰值功率跟踪的具体方法。该方法先根据模糊自寻优控制器的输出计算太阳阵电压的参考值,然后将此参考值与太阳阵的实际输出电压相比较,得出的误差信号去控制脉宽调制输出的占空比,以使太阳阵的输出电压达到此参考值。由于参考电压值的算法充分考虑了太阳阵峰值功率点的逼近问题,因此,上述过程多次进行,就能使得太阳阵的工作点最终到达峰值功率点。     

Longitudinal distribution of thermospheric densities and ionization rates in the upper atmosphere of Mars at mid-latitude using MGS ACC data

The Accelerometer Experiment (ACC) onboard Mars Global Surveyor (MGS) measured 1600 density profiles in the upper atmosphere of Mars during aerobraking. These measurements reveal large-scale and small-scale structure in the thermosphere of Mars. Here, the measurements of mass density for 115 orbits (#P0670–P0789) from November 1 to 30, 1998, under spring equinox and medium solar activity conditions (average F_10.7 ∼ 137) during phase 2 of the aerobraking in the thermosphere of Mars at different altitudes and longitudes are presented for northern mid-latitude (17–42°N) in the dayside atmosphere using ACC onboard MGS. From these mass densities, the neutral densities of different gases are derived from their mixing ratios. Using these neutral densities, the longitudinal distribution of photoionization rates and photoelectron impact ionization rates are calculated at wavelength range 1–102.57 nm due to EUV and soft X-ray radiation under photochemical controlled region using Analytical Yield Spectrum approach (AYS). These conditions are appropriate for MGS Phase 2 aerobraking period from which the accelerometer data is used. Under the photochemical equilibrium condition, the electron density near the peak varies as the square root of the total peak ionization rate. Using this fact, an attempt is being made to estimate the mean primary and secondary peak electron density by averaging the longitudinal variations of total peak ionization rates in the northern mid-latitude (17–42°N) ionosphere of Mars, as there is no radio science measurement at this latitude region by MGS.     

Feedrate scheduling method for constant peak cutting force in five-axis flank milling process

It is extremely important to select appropriate feedrates for the stable machining of parts with ruled surface in modern aviation industrial applications. However, the current studies take too much time to achieve this goal. Therefore, this paper presents an efficient feedrate optimization method for constant peak cutting force in five-axis flank milling process. The solution method of the instantaneous undeformed chip thickness (IUCT) is proposed using least squares theory with the cutter entry angle and feedrate as variables. Based on this method, an explicit analytical expression of the peak cutting force for each cutting point is established. Furthermore, a feedrate scheduling method is developed to quickly solve the appropriate feedrate under constant peak cutting force. To verify the proposed IUCT model, the fitting IUCT is compared with the accuracy data at different feedrates. Additionally, some experiments of five-axis flank milling are conducted to demonstrate the effectiveness of the peak force model and the feedrate scheduling method. And the surface roughness before and after feedrate scheduling is detected. The results show that the proposed feedrate scheduling method can quickly adjust the feedrate and ensure constant peak force during machining. At the same time, the surface quality is kept at a high level.